I think the first step would be a decent exhaust. Any two stroke exhaust builder should be able to build you something that's in the ball park of running right. You could also play with the length of the current exhaust, to see if the exhaust pulses can be timed more correctly to this engine, a first step could be making it a lot shorter.. It could explain those nasty backfires if you dont have Reed-valves fitted. But generally speaking 2strokes need the exhaust pulses to arrive exactly in time to create low pressure to pull gasses in the cilinder faster and high pressure to prevent fresh mixture to be pulled out of the exhaust port before it closes. Best of luck
You are right but not on this type of engine, 4 piston 2 cylinder. You don't need good exhaust because when the "exhaust cylinder's" piston closes the exhaust port, second piston on inlet side will close transfer port little bit later. These engine did not suffer from escaping fresh charge into exhaust as much as conventional two stroke, where good exhaust is a need.
Two strokes ARE Rocket Science-the real wizard of two stroke tuning back in the late 1940’s and onwards into the 1960’s and 70’s was Walter Kaaden who WAS a rocket scientist and worked for MZ. He was the first person to really understand how the pressure waves worked and how to harness them to make much more power. Back in the early 2000’s when I was racing a Yamaha TZ250D we called the team ‘Rocket Science Racing’.
@@chrisjohnson4165 Yes, not an armchair mechanic here. I spent 6 years working exclusively full time on 2 strokes many years ago, street bikes and racing engines included before moving on to aviation. During the 70s, Yamaha 2 strokes were frightfully competitive in the racing world. How many remember the small Yamahas being dominant in the open road racing classes? These bikes were near unbelievable in their performance.
I won't go into family history but let's say I am unusually well versed in the do's and don'ts of scratch-built two cycle engines. First off you have to have DOUBLE LIP seals on any shaft entering/exiting a crankcase-scavenged 2 stroke. This includes between two crankcases as well as the PTO and magneto ends. Second look (and smoke-test) your "piston valves" for sealing. Don't assume that just because you can see the piston closing off an inlet, transfer or exhaust port port - that is is not leaking like crazy. Lastly I recognized your engine as two 125cc Puch twin-singles grafted together straightaway. As an aid to troubleshooting you should borrow a stock and standard 125cc Puch and check it's port timings and see if yours are nearly the same. Finally - and this may seem far-fetched to you - I have experience with ancient T-head 4-strokes which naturally exhibit "charge stratification" in the combustion chamber. (In fact this was an advantage when ignition systems were terribly weak and L - head engines refused to run stably at all) Historical artifact or not - you may well consider having two spark plugs in each combustion chamber similar to a Wankel engine which has that same feature. Possibly as you rev your double-Puch the place at which the mixture is ignitable is moving away from your single spark plug's location.
One more thing - while you are trying to get it running - fit each cylinder with independent exhaust. I suggest each exhaust port have about a foot of straight pipe and then be led into a simple "no effect" expansion chamber such as a recycled propane or freon tank fitted with an outlet about 75% as big as the inlet. This one thing could easily be the entire problem you are having.
Many of the comments are pointing out the exhaust system as being faulty and they are certainly correct as how the system now stands. It certainly is not ideal, but I’m not sure that it’s causing the severe issue which you’re seeing. As a note - I worked as a mechanic for a Yamaha and Bridgestone dealership in the two stroke days. We on occasion would work on older bikes. This specifically referring to twin cylinder two stroke engines fifteen or so years old. A twin cylinder weak point was the crankshaft center seal which isolates the two crank chambers from each other. As one piston is coming down on its crankcase compression stroke the other is moving up on its intake stroke. Any air leakage between the two would result in a very sick engine. I’d be surprised, considering the age of the Puch if that crank center seal is still doing its job. Bridgestone had a problem with center seals in the early 70s, resulting in a good bit of warranty work. Often the older Yamaha bikes were not worth the potential repair bill. The symptoms which you’re seeing are hauntingly familiar. Unfortunately the repair is not simple. The crank will need a press for disassembly and reassembly, and it will then go on centers for alignment with a hammer. If your engine were mine, I’d rig up an adapter plate for the carb flange and apply a few pounds of air pressure to the crank chambers checking for air leakage one crank chamber to the other. If that’s ok, fingers crossed, move on to ignition timing. If you’re lucky and have a timing spec given in so many mm piston movement before TDC, this can be easily done with a dial indicator through the spark plug hole. If the spec is given in degrees before TDC, you’ll have to go through the whole exercise of finding crankshaft rotational TDC and then using a degree wheel. Timing is critical. I would then remove the present exhaust piping and jet the carb for what I guessed as a bit too lean. As far as simply running, a 2 stroke is much more tolerant of a lean mixture than a rich. However a caution, it will run hot on the lean mixture if put under load. With these three criteria met, a serviceable crank center seal, proper ignition timing, and a leanish mixture; the engine should operate adequately for the display stand purpose. The engine will run with open exhaust ports but it will sound like two chainsaws running side by side. A chainsaw operates with near an open exhaust port. Everyone is absolutely correct in regards to the tuned exhaust advantages and this would definitely apply if the engine were to be installed in an auto and to expect any performance. For your display purpose, I would lean towards sound control. The tuned expansion chamber system will split eardrums. I would try Y’ing each cylinder’s exhaust ports together and then through a small glass pack type muffler. A Y And a muffler for each cylinder pair. One last thought and it’s something which I would occasionally run into. We used to build and tune 2 strokes for racing. Now and again we would get an engine where an amateur had taken a Dremel grinder to the internal cylinder and piston porting in hopes of more horsepower. In general not a successful outcome. Expertly done, these modifications can be successful, but now the matching expansion chamber exhaust is critically important and most gains will be in the higher RPM ranges. It’s an art. Hopefully, your engine’s porting has not been altered. This is the sort of project when success is finally achieved; one wipes one’s forehead and exclaims, “Well that was certainly an adventure!” Good Luck For what it’s worth - I inadvertently posted this in Ivan’s second report on the Puch project. I discovered (new to me) that one can use the edit function to copy text from one video and transport that text to another video. I will admit that I’m sharper on 2 strokes than I often display in navigating various You Tube features.
Bloody brilliant Ivor, smoke and back firing, noise and kerfuffle, I love it. The answer will come I am sure, put it to one side for a while and when you come back the answer will be there.
From an old time 2c mechanic: Two strokes have a smaller throttle slide cut-out than a comparable 4c. I'd guess that a Mikuni carburetor off an old Suzuki T500 twin would be ideal for a bench-mark unit to make the engine have proper carburation. A carb with too large a bore will not allow good mixture draw or atomization and the consequential lean/rich fuel draw will cause the engine to spit and backfire.
@@davebaker9128 They were primo bikes in their day. Only thing going against them was the eventual deterioration of the inside crankshaft seals and they would start sucking transmission oil.
Thanks for the update. It’ll get sorted out eventually. It’s frustrating but you have the right idea. Set it aside and get in with another project. I find that when I do that, occasionally I’ll have an epiphany and the problem is solved. Cheers Mates from across the pond !
Back in the sixties I worked for a SAAB dealer and we had to tune those 2 stroke models- setting the timing with a dial indicator on the top of the piston. If anyone asked how to spell SAAB, we always said SOB.
Hey old un' I love the honesty. Seeing you on your knees I thought you were praying for some divine intervention. Poor sod. You will get there though Ive' The carb situation doesn't help I know but to my thoughts, the engine doesn't want to really rev. That may be though because it is cold and the mixture is all to cock. Best wishes from the Black Forrest contingent.
Something which I forgot to mention regarding ignition timing. On some engines wear on the points rubbing block can be critical for achieving proper timing. The reason being that on some there is little and occasionally on others no provision for moving the points rotationally to achieve proper timing. Precise timing is set by adjusting the point gap. If the rub block is worn beyond specs, one finds it impossible to set proper timing while maintaining the point gap within the allowed range. This is typically on older vintage stuff.
Good to see it run, the remark " and we will send another month trying to tune it", made me laugh. Good production from your new film maker. Excellent camera work and high quality picture, only thing I dident like was the opening music continued on for to long and disrupted Ivan's voice over. That said great to have you back.
I had a 2 cylinder 2 stroke that ran similar to yours. Turned out the key way on the flywheel had bent from a square to a very subtle Z if you can picture it so the timing was fractional out plus one of the rods had a minute compression bend don't know which happened first but both together put my timing out enough to make it blow back through the carbatooter . Good luck
I don’t know all about the two-stroke intricacies but i have one thing popping up in my mind when i see this: Isn’t a multiple cylinder two-stroke engine supposed to have a separate exhaust pot (read: tuned expansion chamber) pr. cyl. in order to scavenge each combustion chamber correctly? In your case: Using exhaust pipes collected into a manifold; As long as a two-stroke has no exhaust valve, the exhaust port is open for back pressure from the exhaust generated by the other cylinder(s) as the piston travels down and reach the inlet port. That will impede the flow of mixture entering the inlet port and cause the problems you have, backfiring and all that s…t?
I think all the racing two strokes I've seen have an exhaust for each cylinder. The only exception I can think of is the Trabant made in the former DDR.
Great Chanel Ivan I'm a great fan. I'm also a mechanical engineer and build race engines and restore vintage and classic motorcycles . Mostly two strokes . The problem is in the ignition system. Points fire the plugs when opening breaking the circuit collapsing the magnetic field which then generates the high voltage in the secondary field . ( but you know this ) . If you have a bad condensor or too high voltage ( one other comented on this ) when the points close making the circuit establishing the magnetic field there can be sufficent magnetic flux to fire the plug .and this will happen when the transfers ports are open with a nice mix of fuel and air flowing by hence the backfire into the crankcase and out the carby. It is not your 4 into 1 .thats on every 4 cylinder outboard motor. I've been to the NSU museum in Germany and all there race split singles had straight pipes . Cheers Howard.
Hi Robert. Intresting that you think a reed valve and variable timing will prevent phantom firering when points close ? Can you explain how that works ? Cheers Howard
Hi Robert. The donor design for Ivan's split single is the 4 cylinder Puch designed in 1935 . Walter Kaaden the father of two stroke exhaust tuning started his work on expantion chambers for racing in 1947 . I have several 1930,s two stroke motorcycles in my collection that with bikes covering the 30,s 40,s 50,s 60,s and 70,s it wasn't till the 1960,s that any attempt was made to tune the exhaust sytem up till then it was a straight pipe to a muffler with a torturous path to reduce the noise . About 80% of the comments tell Ivan it the exhaust system and to have single pipes or expantion chambers ? That would be fine if Ivan was looking for more power .but he is trying to diagnose a back fire and poor running issue. My 1980,s 140hp Chrysler ski boat had nothing more than drilled row of holes for exhaust ports into a common plenum discharging down the leg under water .no pipes or expantion chambers needed . Cheers Howard
@@howardsway7788 Hi Howard Is the port timing on the engine set up so no errant spark from another cylinder can enter thru the exhaust port Causing it to interfere with the intake charge? . As a Yank I apologize for the poorly written comment I posted. Interesting old engine I imagine Ivan will have it running properly soon. Thanks to your comment now I want to read the book on Puch engine development as it was designed to save fuel. I tend to modify them the In the other direction
@@AtlasLathe Hi Robert. The exhaust port timing is set up so you can't cause backfiring across into the other cylinders . At first glance it looks like a 4 cylinder motor with 4 exhaust pipes ( because it is ) BUT in reality it is in effect a two cylinder engine with each side split in two with a common combustion chamber . The paired cylinders are 180 degrees apart . With very long stroke ( compared to modern two strokes ) as the transfer ports are on the oposite side cylinder to the exhaust ports .this allowed the exhaust ports to be in the bottom 1/3 of the stoke . With the 180 degree crank it is impossible to cross feed a backfire into the other cylinder because the exhaust ports are never open together . Just to add intrest they use two exhaust ports per cylinder to give a wide squat cross section area . The ports are spread apart so there is plenty of cylinder wall to carrie the rings across the port .hence the 4 exhaust pipes on a twin split cylinder engine . Ivan will have it sorted soon . I'm over in UK soon for work might catch up with there classic racing scene Cheers Howard
Great to get it running ! I think you might need to look at the exhaust system . There might not be enough back pressure . Two Strokes are very fussy when it comes to exhausts.
My first thought too: They are dependant on the expansion chamber to draw the fuel mixture into the cylinder as well as drawing out the exhaust. The position of the chamber from the port is critical too, along with the timing of the closing of the intake over the exhaust ports.
My thought as well. I would suggest trying it with four seperate pipes to start with, and if that shows improvement, then start playing with tuning the lengths etc.
I chime in with another exhaust comment, as a rider of over 40 years. An expansion chamber exhaust is worth a try. There have to be many web plans for same; it could well cure the chuffing back through the carb.
Perhaps a diaphragm carburetor would be better for running a two stroke engine, It would be better for fuel delivery i believe, as always your program is intellectually stimulating, thanks for the unique projects, i am a weird engine fan for a lifetime,👍
I've had a similar problem with a soviet chainsaw engine from 1976, where it would backfire through the carburetor. The problem turned out to be the piston. It was a standard aluminum piston but the ring retainers were made of brass and were riveted through the piston into the ring grooves. Over time the retainer loosened up and allowed combustion gasses to go through the ring groove and under the piston, which would cause it to backfire. The fix was quite easy, i just made a tool to get into the piston and behind the ring retainer to peen it over some more and that fixed all of my problems.
If you need help with the engine , perhaps if that lovely Mr Millyard is watching this he could offer some advice . A collaboration between you two is something I'd pay you tube to watch . Keep up the good work .
I remeber years ago putting the cylinder head on the wrong way around on a CZ or MZ and it gave me the same issues of spitting back, it looks like the bolt pattern may allow this on this engine. Hope you continue to pursue it and get this one to run properly.
The heads are on backwards. The spark plugs go to the rear , over top of the intake cylinders. The engine is also turning backwards. These engines rotate counter clockwise. Clockwise rotation causes the intake ports to open far too early and the exhaust opens late. The ignition timing will also be off if it was set for clockwise rotation. Super cool engine. I hope it gets sorted. Cheers Fred
It is good to hear you have a new camera person on staff now. I am sure with time, you will get that rather bizarre engine sorted. It is good to see you back online. You always have the coolest stuff.
I wouldn't say this is the case here, but that engine sounds as if it is over oiled, running with an "almost missfire" at a large throttle opening. Spluttering (or 4 stroking) we called it 45 years ago; on my Yamaha 50cc it was easily cured by adjusting the autolube pump. Also sometimes caused by over rich mixture, which could point to your carb...
I think it is important that the pistons are in the correct cylinders, two are slightly longer than the others, if they are visa versa they will push the charge back into the previous cylinder instead of the exhaust. It was 1971 when I last worked on a Puck split single and the memory is a little vague.
No background music while your talking please, some of us deaf old gits find it hard to hear with background noise. Other than that, love seeing what you are up too again.
Hi , I have had experience with outboard motor ( two stroke) that commonly spat back through the carb ,this was caused by a lean mixture at low speed, the spit Back stopped when engine was under load , try putting a load on the engine. Roger in Norfolk.
From what I can see in your video the exhaust is a straight through pipe with no expansion chamber 🤔 in my experience all 2strokes need the expansion chamber to create back pressure and I think that this will make the engine run better also 🤔🤘 I've not seen one of these engines but have worked on 2strokes all my life , from motorbikes to outboard engines from 2hp to 250hp 😉 good luck with the build 🤘
great content guys! Nice double piston puch like engine. Looks like the intake timing is way to high, so maybe the crank is wrong way mounted? exhaust piston is now the intake piston viceverse?
Two stroke engines the INTAKE goes thru the crankcase NOT the cylinder head like normal engines! 👍👍 The two stroke sounded like MAYBE the sparks were out of time ( i could be completely wrong ).
I would look closely at the ignition system for A. possible bad condensers out of the box (seen that more than once) B. too much voltage to the coil(s) causing the points to arc (install ballast resistor). I would also look into maybe turning the heads around with the plugs on the opposite side. It looks like they'll go on either way from what I saw with the bolt pattern. If the plugs are over the intake side, it's possible they're firing before the ports are fully closed and causing the backfire through the carb. (Overvolting the coils will give a similar condition though). Just a few ideas.😉
With your 4 stroke 2 cylinder engine, I think it would have been better if the crankshaft was made so the both pistons were at the top at the same time. This is because it takes 720° of rotation for each cycle and the second cylinder should be firing 360° after the first cylinder... with this crankshaft set up you have created, the second cylinder is only 180° after. Just my thoughts... fascinating videos 👍🏻
I don't know how, but you are setting fire to the 2T mix in the crankcase. You can see all the soot in the bottom crank case halve. It looks like some sort of ignition misfire happening when the inlet ports are open and flashing right down through the entire crank case. Is there a chance the ignition coils are interfering with each other ? As a test completely separate the ignitions so they are like two completely separate motors. the only common thing is the points cam. The wires to the coils 2-3 inches apart, the coils a foot apart etc. Also mark the crank pulley for tdc for each piston pair. Start the motor. Then put timing light on each plug lead and check the ignition is happening correctly on each pot and keeps doing so as you bring the rpm up. 2nd also check the opposing cyclinder isnt being fired at bottom dead center by EMF or something weird. 3ndly 70's 2T motor cycles didn't run any mechanical ignition advance. I'd disable any advance mechanisms. Then using a dial indicator have the points close about 3mm before top dead center btdc. 5th Also is it possible the exhaust merge pipe is setting fire to the opposing cylinder , while the exhaust port is open and the un-scavenged 2T mix is wofting out of the cylinder. Maybe seperate the left and right pipes. 6th Also, 2 strokes can run forward or backward , they don't care much (a back fire can result in motor running backward and they keep running until the kill switch is pressed). That crank seal direction won't matter, the tiniest bit of air it might suck is not going to cause this issue. good luck.
Are the cylinder liners removable or is it all part of the barrel? Just wondered if a transfer port or something is at the wrong height? Are the piston heights the same or is one taller than the other? You mentioned the reed valve being swapped out and not making a difference but surely if the reeds were closing properly it would be impossible for it to back fire through the carb? I’m no 2 stroke expert, just throwing ideas at it in case one of them helps find a solution. Great Chanel guys. Love your work and really appreciate you taking the time to share it with us.
I think mostly induction. Maybe crankcase pressure overcoming the reeds? Transfer port timing? Problem is it could be a combination of things, but it shouldn't be able to blow back through the carburettor..
maybe there there is to much airflow in the exhaust, could try and put a temporary restrictor to restrict the airflow of the exhaust. Great videos keep it up.
My 10 cents worth is that with the combined exhaust the flame from from cylinder "B" is travelling out the pipe and a bit of it travels back down the pipe of cylinder "A" (when cylinder "A"s') transfer ports are open. Thereby igniting the air/fuel right back through the system. Ken Brough
Most two stroke engines need a little back pressure via an expansion chamber (exhaust) to even run , the down side to this is the exhaust will need to be tuned to the engine and maybe custom made if the engine isnt stock..
Not sure if it's been suggested but have you contacted Sammy Miller in the New Forest, he's got an amazing variety of weird and wonderful stuff including split single (ok yours is a split twin) strokers.
Glad you found the comments useful, I am sure most of us meant them in the nicest way. The engine is a puzzle as it is not conventional. Chuffing out of the intake does suggest that something about the timing is marginal but I had another random thought, are you setting it for the wrong piston? IE before the wrong TDC? Presumably the ignition timing should be just ahead of the second piston? I know nothing about these engines, it did sound good on song but the chuffing suggest it is firing far too early before the intake transfer port is closed.
Another possibility is a plugged exhaust or exhaust port- both are somewhat "normal" problems to have on older two strokes. Notice that the engine doesnt begin popping out the carb right away, but then when it does, it looks like exhaust.
Right then Mr. Dutton. That certainly appears to be two SG 250 Puch Twingles lashed together. I reckon you want to get your hands on one of those and do a comparison as to port timing, perhaps they mucked with that when they built up this prototype (although I suspect the cylinder liners are simply stock Puch liners). As well, your carburettor is completely crap, not even in the ballpark mixturewise. I'd have a hunt for two carbs off an SG and be done with it. Tell you what though, even two SG250 engines won't pull the skin off a rice pudding. The bike would do perhaps 70 mph (nah it wouldn't) if you wrung its fookin neck and laid down like Rollie Free. I personally don't believe the oil seal orientation made any difference. Two stroke crankshaft seals are somewhat special as they are engineered to contain pressure and prevent vacuum leakage. If you're using plain old seals you really want two slim seals installed back to back. That'll do the trick and I have actually done this. Are you ABSOLUTELY certain it is turning the correct direction? Virtually all two strokes will run backwards, just not very well, although that's mostly to do with ignition timing. not the reversed rotation per se.
"It's been a bloody nightmare" Possibly why it didn't make it past the concept and development stage? Took too long to get working and running well enough to make it to the next stage - especially with working four stroke designs in competition.
I've been enjoying your endeavours with odd engines. Good clean fun! Keep it up please. Just one little complaint though, regarding the cliche that petrol heads all like heavy rock and electric guitar. I'm certainly one who doesn't, and was most glad when it finished. Cheers.
Hello again. As I mentioned before, it is going to be the correct mixture in the engine that matters. About 40 years ago a friend and I built a single cylinder scooter engine. We fitted a very expensive Fish injector. When it arrived the injector turned out to be just a big bore vertical tube with a simple butterfly and a, specific bore, sideways tube (jet) to supply the fuel. No float chamber. The fuel was delivered by gravity and had to be turned on and off by the tank tap. If you forgot the engine filled with fuel! This did give a large increase in power. Obviously the quality of the carburettion was not important - just the amount of fuel! The porting in the engine, which presumably has not changed, is fixed so that only leaves the exhaust which would usually be of an expansion/extractor type which would help pull the exhaust out and the new mixture through. These tuned exhausts are/were a bit of a dark art. My father in law was a kart builder and racer of some success who built his exhausts by trial and error - I think. His engines were just single cylinder Villiers 9E's with larger Amal carb. with the porting tuned as well. It might be worth trying your engine without the exhaust pipe to see if there is a difference. Good luck
Hi, the backfire through carb could be poor seal between the two crankcases in the middle of the crank allowing pressure to come back through carb. You may need two seals back to back to stop this happening.
bing a 2 stroke it needs an expansion chamber on the exhaust to get the right backpressure.. the way its spluttering indicates the backpressure builds too much until it pops out the inlet, get a 2T exhaust system off a motorbike anf try that im sure it will massively improve things ..Love this chanel BTW and the things you all do :)
I wonder if your middle crank seal is leaking letting the compression and drawing vaccume between the two bottom ends transfer. It doesn't look like there is a rubber seal in there , I have seen snowmobile engines with a labyrinth seal between the two sides of a crankshaft but I don't see that in yours either... Hugs from Canada
well done Ivan , John and a big thanks to the new video production person cracking job , looking forward to the next instalment , ps i have always had a love hate relationship with any thing 2 stroke they either work real well or just a complete nightmare
Have you tried an exhaust with an expansion chamber? This will cause the exhaust pulse to help pull in the incoming charge and keep it from blowing back through the carb. Just a wild thought....?????
A normal 2 stroke engine can run in either direction, all that changes is the ignition timing. A twingle is different since the exhaust and transfer ports are in different barrels. That means that it is possible to have the transfer ports opening before the exhaust if the engine is running backwards. The result would be blowing back through the carburettor. I would have another look at that before dismissing it completely. Alternatively, is it possible that the barrels are reversed? I'm unsure if the primary con rod is on the transfer side or the exhaust side but if they are the wrong way round it would throw the timing out completely.
Exactly my thoughts, too. Also i noted that the exhaust pipes doesn’t look like they offer back pressure of any kind. The design of the transfer ports could also be relying on this back pressure so maybe also a potential culpritt ?
Racing Scotts had straight pipes with no issues, indeed ran worse with expansion chambers, also many Aero engines. Maybe induction is the issue? Is it reed, rotary valve or piston ported?
Got to agree with a lot of other comments re exhaust I’m sure an expansion pipe would help , I used to have the formula for working out the cones somewhere
it implies from the flow that's it's backwards it should never be able to have exhaust smoke from the carb as there should be a piston in the way or the ports should be shut. are the pistons " handed" ?
Suggestion: use the carb off a Rotax two stroke engine. They fit to the manifold byway of a Felix pipe and jubilee clip. The miss fire appears to be something to do with the timing. One cylinder might be out of phase. Best of luck. Graham P.
How are the points cam timed? Did someone pull the cam off to replace crank bearings & get it back on wrong. Some 2 strokes don't use a key way for alignment of the points cam. If that's the case good luck on checking & correcting.
I'm pretty sure it needs separate exhaust pipes, as suggested below. Never seen a multi-cylinder two-stroke with a common exhaust system. One cylinder opens the exhaust port on the Powerstroke while the other is closing it during the intake stroke, and then there is an open connection to the carb causing the backfire. The easy way to test is to remove the exhaust pipe and start it up.
Two stroke cars do, but design will be critical. You want it to push back enough to stop the fuel air charge escaping out the exhaust but not enough to backfire like this! One for the maths wizards I think. Could do 3 separate expansion chambers, each with reed valves where they join to one common pipe? I wonder if that'd work
2 stroke expansion chamber exhaust science . it will take you a long time to get the shape and length right . good luck old boy . from nassau long island usa
I had a Puch 175, not a fussy engine it ran 24:1 on sae 30 with worn pistons.The misfire sounds like ignition. Two other possibilities, maybe it needs 2 carbs? no one ever made a double twingle afaik. secondly could the compression be too high? love the channel, it's all real.
I have a love/hate relationship with 2-strokes, they're wonderfully simple and can run and sound fantastic when things are going well, but they're finicky, high-maintainence little beasts! apart from very early examples (full of cast iron and bronze-bushes) they've got a limited lifespan too! I reckon the backfiring could be down to the exhaust, most 2-strokes rely heavily on the resonance of the pipe to run, and keep the gasses moving in the correct direction. although older 2-strokes (pre-war especially) are quite happy without a resonating pipe I think if you made something up along the same lines as was fitted to the puch bike engines, you'd at least eliminate that issue.
Iirc 29 inch pipe length for individual pipes from the piston should give the right reversion pulses from an open ended pipe.... the reflected pulse should arrive back at the right time..
I've seen Suzuki Water Bottles with bloody light years on them running merrily along. 70,000 - 80,000 miles was not particularly remarkable if you kept oil in the injection tank. Certainly I've seen regularly used outboard motor two strokes that were 50 years old and had never been to bits.
@@scheusselmensch5713 It all depends on the care taken when operating i suppose, most of the 2-strokes I see are thrashed within an inch of their life and only get attention when they won't thrash any more! there's plenty of them out there that have a LOT of hours on them and are still ticking, but the vast majority tend to live fast and die young. I'll still stick to the old iron though, it smells of castrol and makes better noises!
@@theafro life of a 2 stroke all comes down to feeding and maintenance. Use proper fuels and oil warm them up properly and provide the proper maintenance when required and they will run forever
@@holmes1956O the trouble is, that the majority of 2-stroke users nowadays are either young lads on scooters or arborists with chainsaws/brush-cutters, neither category are known for mechanical sympathy!
The engine design is pre WW2 . back then the racing DKW split singles ran on open megaphone exhausts , the post war EMC racers did the same, this engine is a pair of EMC built Puch design twingles so does not need expansion chambers. I ran my Puch 175 with the exhaust internals removed (open megaphone) the noise was incredible!! but it ran fine. I put another Puch engine in a home made scrambler with a 2 into 1 exhaust ending into an old car silencer !! that ran great too. This was back in the mid 1970's LOL
I'd be inclined to try an expansion chamber type exhaust on it, I don't know a huge lot about 2 strokes but somebody did tell me once that "the exhaust is half the engine" with them.
To all the folks in here saying it needs a proper exhaust, you are both right and wrong. I have been around the good old 2 stroke engine in snowmobiles and motorcycles for about 40 years now. For best performance at a given rpm yes a tunned pipe is needed bit just to run on a stand they should run just fine even without a manifold. Will they have power? Probably not a lot but will still idle and rev just fine. My thoughts on this engine is ignition or port timing is off, most likely ignition. Someone mentioned spark plugs and I certainly would start there.
On some of my 2 strokes I found playing with spark plugs improved thing alarmingly and playing with the exhaust design ,if you can remember the Arial Arrow it went like a rocket with what we called crackle pipes fitted which altered the flow of air through the cylinders It maybe an idea to talk to Villier go kart owners as they had the art of exhausts off to a tee ,the 9E bottom end was the engine that took a few titles in its time
I suggest trying slightly earlier ignition timing, and also sparking plugs with precious metal electrode tips. I think the combustion is taking place too late and/or too slowly, so it is not completed by the time the transfer ports open. I suspect that this design of engine may need more ignition advance than a conventional engine, because the flame has further to go from the sparking plug to the far sides of the cylinders. Also regarding the direction of rotation, the split layout gives asymmetric timing of the transfer and exhaust ports and this has to be in the right direction. If you imagine the engine in a motorcycle then if it is turning in the same direction as the wheels the transfer ports need to be on the front cylinders and the exhaust ports on the rear cylinders; vice versa if the engine runs in the opposite direction to the wheels. If the engine is running in the wrong direction, the transfer ports are possibly opening before the exhaust ports; I think this would cause a strong tendency to spit back.
Further to my previous comment, I think it is possible to see from the video that the positions of the transfer and exhaust ports are correct for the direction of rotation, assuming that it is clockwise as seen from the end with the ignition system.
Yet another thought: what is the definition of top dead centre on a "split" engine? There is a point of maximum compression, at which the piston on the exhaust side is already on the way down and the piston on the transfer side has not yet reached the top of its stroke. I think this point of maximum compression has to be regarded as top dead centre for the purpose of determining suitable ignition timing. You could find it accurately with a U-shaped transparent tube with some oil in it, attached at one end to a bung that fits into one of the sparking plug holes.
excellent video, interesting problem ,for the exhaust smoke to come out the carb the pistons and ports need to be open on both cylinders and that would happen, I'm assuming a intake piston and a exhaust piston with a shared combustion chamber, it looks like you are either missing a valve on the intake or ....you have an open intake it couldn't be that there is supposed to be an air filter or intake pipework so the moving air mass is involved in the scavenging, at what point does the plug fire? and is it a wasted spark system with the wasted spark igniting the remains of an over rich combustion event ? I would stick a scope on the timing to be honest it's so close
Are your primary pipes from the cylinder to the collector box too short causing exhaust gases from one cylinder to "short circuit" into the other cylinder causing the misfire as it looked in the video like the exhaust pipe would shake when the misfire occurred, also the collector box for the primaries looked very small which could be exacerbating the problem as the exhaust is remaining "pressurised" from one cylinders exhaust event to the next cylinders.
I've been doing a lot of thinking about your 2 stroke backfiring through the carb. You need to get rid of your wasted spark on the exhaust stroke. What is happening is the fuel is firing before the piston passes the port. This thought came to me in a dream around 4 am in the morning and I woke up and I'm sitting texting you on my phone in CoArmagh were I live before I forget. Please let me / us know how you get on with this theory / dream. Regards Alan Winter
Basicly one piston controls the intake function and the other controls the exhaust. This allows the port timing to be asimetrical so you can favor port opening and closing for best power . Normal single piston 2 stroke port timing is always a compromise , porting for max power usually kills the bottom end. Reed valves or rotory valves on the intake and tuned exhaust are ways improve the power band while still trying to obtain max power with a usuable power band.
@@dog8nut I don't think so as surely you would only have 2 exhaust ports for your arrangement. I think we simply have a 4 cylinder 2 stroke, arranged like a v4 or parallel 4
@@psk5746 The orignal PUCH design used twin exhaust ports on their 2 piston ONE COMBUSTION CHAMBER engine. So what we have in this case is a 2 cylinder 4 piston parllel twin with 2 combustion chambers. Still with 2 exhaust ports/pipes per cylinder.
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It was a relief when the music was turned off and we could just hear Ivan talk.
I must have something with sound on my computer, as I often don't hear the music people comment about.
Kick it some more Ivan.
I think you are onto something there.
gary
I think the first step would be a decent exhaust. Any two stroke exhaust builder should be able to build you something that's in the ball park of running right.
You could also play with the length of the current exhaust, to see if the exhaust pulses can be timed more correctly to this engine, a first step could be making it a lot shorter.. It could explain those nasty backfires if you dont have Reed-valves fitted. But generally speaking 2strokes need the exhaust pulses to arrive exactly in time to create low pressure to pull gasses in the cilinder faster and high pressure to prevent fresh mixture to be pulled out of the exhaust port before it closes.
Best of luck
Just what I was going to ask...
You are right but not on this type of engine, 4 piston 2 cylinder. You don't need good exhaust because when the "exhaust cylinder's" piston closes the exhaust port, second piston on inlet side will close transfer port little bit later. These engine did not suffer from escaping fresh charge into exhaust as much as conventional two stroke, where good exhaust is a need.
Ivan kicking the 2stroke while the 4stroke was chugging along merrily made me laugh far more than it should have
Don't get bored, get even. Keep up the good work.
Two strokes ARE Rocket Science-the real wizard of two stroke tuning back in the late 1940’s and onwards into the 1960’s and 70’s was Walter Kaaden who WAS a rocket scientist and worked for MZ. He was the first person to really understand how the pressure waves worked and how to harness them to make much more power. Back in the early 2000’s when I was racing a Yamaha TZ250D we called the team ‘Rocket Science Racing’.
Excellent content!! I don't care at all for the music! I enjoy Ivan's commentary.
The music and graphics make this look like an American "reality" tv show.
Still the coolest content though.
Nice to know that armchair mechanics are not entirely useless. Well done, chaps.
Yes, but don't forget that some of us were mechanics a long time ago!
@@chrisjohnson4165 Yes, not an armchair mechanic here. I spent 6 years working exclusively full time on 2 strokes many years ago, street bikes and racing engines included before moving on to aviation. During the 70s, Yamaha 2 strokes were frightfully competitive in the racing world. How many remember the small Yamahas being dominant in the open road racing classes? These bikes were near unbelievable in their performance.
I won't go into family history but let's say I am unusually well versed in the do's and don'ts of scratch-built two cycle engines. First off you have to have DOUBLE LIP seals on any shaft entering/exiting a crankcase-scavenged 2 stroke. This includes between two crankcases as well as the PTO and magneto ends. Second look (and smoke-test) your "piston valves" for sealing. Don't assume that just because you can see the piston closing off an inlet, transfer or exhaust port port - that is is not leaking like crazy.
Lastly I recognized your engine as two 125cc Puch twin-singles grafted together straightaway. As an aid to troubleshooting you should borrow a stock and standard 125cc Puch and check it's port timings and see if yours are nearly the same.
Finally - and this may seem far-fetched to you - I have experience with ancient T-head 4-strokes which naturally exhibit "charge stratification" in the combustion chamber. (In fact this was an advantage when ignition systems were terribly weak and L - head engines refused to run stably at all)
Historical artifact or not - you may well consider having two spark plugs in each combustion chamber similar to a Wankel engine which has that same feature. Possibly as you rev your double-Puch the place at which the mixture is ignitable is moving away from your single spark plug's location.
One more thing - while you are trying to get it running - fit each cylinder with independent exhaust. I suggest each exhaust port have about a foot of straight pipe and then be led into a simple "no effect" expansion chamber such as a recycled propane or freon tank fitted with an outlet about 75% as big as the inlet.
This one thing could easily be the entire problem you are having.
@@patrickshaw8595 As far as I am concerned , the long answer you gave is imho opinion the correct answer.
@@Chappomusic Thank You you are Welcome.
Many of the comments are pointing out the exhaust system as being faulty and they are certainly correct as how the system now stands. It certainly is not ideal, but I’m not sure that it’s causing the severe issue which you’re seeing. As a note - I worked as a mechanic for a Yamaha and Bridgestone dealership in the two stroke days. We on occasion would work on older bikes. This specifically referring to twin cylinder two stroke engines fifteen or so years old.
A twin cylinder weak point was the crankshaft center seal which isolates the two crank chambers from each other. As one piston is coming down on its crankcase compression stroke the other is moving up on its intake stroke. Any air leakage between the two would result in a very sick engine. I’d be surprised, considering the age of the Puch if that crank center seal is still doing its job. Bridgestone had a problem with center seals in the early 70s, resulting in a good bit of warranty work. Often the older Yamaha bikes were not worth the potential repair bill. The symptoms which you’re seeing are hauntingly familiar.
Unfortunately the repair is not simple. The crank will need a press for disassembly and reassembly, and it will then go on centers for alignment with a hammer. If your engine were mine, I’d rig up an adapter plate for the carb flange and apply a few pounds of air pressure to the crank chambers checking for air leakage one crank chamber to the other. If that’s ok, fingers crossed, move on to ignition timing. If you’re lucky and have a timing spec given in so many mm piston movement before TDC, this can be easily done with a dial indicator through the spark plug hole. If the spec is given in degrees before TDC, you’ll have to go through the whole exercise of finding crankshaft rotational TDC and then using a degree wheel. Timing is critical. I would then remove the present exhaust piping and jet the carb for what I guessed as a bit too lean. As far as simply running, a 2 stroke is much more tolerant of a lean mixture than a rich. However a caution, it will run hot on the lean mixture if put under load. With these three criteria met, a serviceable crank center seal, proper ignition timing, and a leanish mixture; the engine should operate adequately for the display stand purpose. The engine will run with open exhaust ports but it will sound like two chainsaws running side by side. A chainsaw operates with near an open exhaust port. Everyone is absolutely correct in regards to the tuned exhaust advantages and this would definitely apply if the engine were to be installed in an auto and to expect any performance. For your display purpose, I would lean towards sound control. The tuned expansion chamber system will split eardrums. I would try Y’ing each cylinder’s exhaust ports together and then through a small glass pack type muffler. A Y And a muffler for each cylinder pair.
One last thought and it’s something which I would occasionally run into. We used to build and tune 2 strokes for racing. Now and again we would get an engine where an amateur had taken a Dremel grinder to the internal cylinder and piston porting in hopes of more horsepower. In general not a successful outcome. Expertly done, these modifications can be successful, but now the matching expansion chamber exhaust is critically important and most gains will be in the higher RPM ranges. It’s an art. Hopefully, your engine’s porting has not been altered.
This is the sort of project when success is finally achieved; one wipes one’s forehead and exclaims, “Well that was certainly an adventure!” Good Luck
For what it’s worth - I inadvertently posted this in Ivan’s second report on the Puch project. I discovered (new to me) that one can use the edit function to copy text from one video and transport that text to another video.
I will admit that I’m sharper on 2 strokes than I often display in navigating various You Tube features.
Enjoyable as always but would have been better without the "music"
yes please no "american muscle car" background track, that's strange
Agreed. I try to listen to the story, if I want loud music I go to a rock concert.
Yeah it sounds like the sort of rubbish you get on american telly
Yup. The music is very irritating.
+1, lose the music please.
Bloody brilliant Ivor, smoke and back firing, noise and kerfuffle, I love it. The answer will come I am sure, put it to one side for a while and when you come back the answer will be there.
From an old time 2c mechanic: Two strokes have a smaller throttle slide cut-out than a comparable 4c. I'd guess that a Mikuni carburetor off an old Suzuki T500 twin would be ideal for a bench-mark unit to make the engine have proper carburation. A carb with too large a bore will not allow good mixture draw or atomization and the consequential lean/rich fuel draw will cause the engine to spit and backfire.
Funny, I had a couple of Suzuki T 20 250cc twins a long time ago
@@davebaker9128 They were primo bikes in their day. Only thing going against them was the eventual deterioration of the inside crankshaft seals and they would start sucking transmission oil.
Thanks for the update. It’ll get sorted out eventually. It’s frustrating but you have the right idea. Set it aside and get in with another project. I find that when I do that, occasionally I’ll have an epiphany and the problem is solved. Cheers Mates from across the pond !
Back in the sixties I worked for a SAAB dealer and we had to tune those 2 stroke models- setting the timing with a dial indicator on the top of the piston. If anyone asked how to spell SAAB, we always said SOB.
Well, we can wait. Let's continue with the other interesting projects!
I really enjoy Your UA-cam channel. You Both are an excellent Automotive Engineers of the highest standard.. Being viewed down here in WLG NZ..
Hey old un' I love the honesty. Seeing you on your knees I thought you were praying for some divine intervention. Poor sod. You will get there though Ive' The carb situation doesn't help I know but to my thoughts, the engine doesn't want to really rev. That may be though because it is cold and the mixture is all to cock. Best wishes from the Black Forrest contingent.
Something which I forgot to mention regarding ignition timing. On some engines wear on the points rubbing block can be critical for achieving proper timing. The reason being that on some there is little and occasionally on others no provision for moving the points rotationally to achieve proper timing. Precise timing is set by adjusting the point gap. If the rub block is worn beyond specs, one finds it impossible to set proper timing while maintaining the point gap within the allowed range. This is typically on older vintage stuff.
You and John are doing excellent work
Well done gentlemen, it sounds good.
Good to see it run, the remark " and we will send another month trying to tune it", made me laugh.
Good production from your new film maker. Excellent camera work and high quality picture, only thing I dident like was the opening music continued on for to long and disrupted Ivan's voice over. That said great to have you back.
that carb blowback might be a reed valve or sleeve valve stuck or mis timed.
I had a 2 cylinder 2 stroke that ran similar to yours. Turned out the key way on the flywheel had bent from a square to a very subtle Z if you can picture it so the timing was fractional out plus one of the rods had a minute compression bend don't know which happened first but both together put my timing out enough to make it blow back through the carbatooter . Good luck
Brilliant!!!!
I admire your perseverance!! Well done guys!
I don’t know all about the two-stroke intricacies but i have one thing popping up in my mind when i see this: Isn’t a multiple cylinder two-stroke engine supposed to have a separate exhaust pot (read: tuned expansion chamber) pr. cyl. in order to scavenge each combustion chamber correctly? In your case: Using exhaust pipes collected into a manifold; As long as a two-stroke has no exhaust valve, the exhaust port is open for back pressure from the exhaust generated by the other cylinder(s) as the piston travels down and reach the inlet port. That will impede the flow of mixture entering the inlet port and cause the problems you have, backfiring and all that s…t?
4 into 1 on a two stroke is going to confuse it!
I think all the racing two strokes I've seen have an exhaust for each cylinder.
The only exception I can think of is the Trabant made in the former DDR.
Great Chanel Ivan I'm a great fan.
I'm also a mechanical engineer and build race engines and restore vintage and classic motorcycles .
Mostly two strokes .
The problem is in the ignition
system. Points fire the plugs when opening breaking the circuit collapsing the magnetic field which
then generates the high voltage in the secondary field . ( but you know this ) . If you have a bad condensor or too high voltage ( one other comented on this ) when the points close making the circuit establishing the magnetic field there can be
sufficent magnetic flux to fire the plug .and this will happen when the transfers ports are open with a nice mix of fuel and air flowing by hence the backfire into the crankcase and out the carby.
It is not your 4 into 1 .thats on every 4 cylinder outboard motor. I've been to the NSU museum in Germany and all there race split singles had straight pipes . Cheers Howard.
Hi Robert.
Intresting that you think a reed valve and variable timing will prevent phantom firering when points close ? Can you explain how that works ?
Cheers Howard
Hi Robert.
The donor design for Ivan's split single is the 4 cylinder Puch designed in 1935 . Walter Kaaden the father of two stroke exhaust tuning started his work on expantion chambers for racing in 1947 .
I have several 1930,s two stroke motorcycles in my collection that with bikes covering the 30,s 40,s 50,s 60,s and 70,s it wasn't till the 1960,s that any attempt was made to tune the exhaust sytem up till then it was a straight pipe to a muffler with a torturous path to reduce the noise .
About 80% of the comments tell Ivan it the exhaust system and to have single pipes or expantion chambers ?
That would be fine if Ivan was looking for more power .but he is trying to diagnose a back fire and poor running issue.
My 1980,s 140hp Chrysler ski boat had nothing more than drilled row of holes for exhaust ports into a common plenum discharging down the leg under water .no pipes or expantion chambers needed .
Cheers Howard
@@howardsway7788 Hi Howard
Is the port timing on the engine set up so no errant spark from another cylinder can enter thru the exhaust port Causing it to interfere with the intake charge? . As a Yank I apologize for the poorly written comment I posted. Interesting old engine I imagine Ivan will have it running properly soon. Thanks to your comment now I want to read the book on Puch engine development as it was designed to save fuel. I tend to modify them the In the other direction
@@AtlasLathe
Hi Robert.
The exhaust port timing is set up so you can't cause backfiring across into the other cylinders .
At first glance it looks like a 4 cylinder motor with 4 exhaust pipes ( because it is )
BUT in reality it is in effect a two cylinder engine with each side split in two with a common combustion chamber . The paired cylinders are 180 degrees apart . With very long stroke ( compared to modern two strokes ) as the transfer ports are on the oposite side cylinder to the exhaust ports .this allowed the exhaust ports to be in the bottom 1/3 of the stoke . With the 180 degree crank it is impossible to cross feed a backfire into the other cylinder because the exhaust ports are never open together .
Just to add intrest they use two exhaust ports per cylinder to give a wide squat cross section area . The ports are spread apart so there is plenty of cylinder wall to carrie the rings across the port .hence the 4 exhaust pipes on a twin split cylinder engine .
Ivan will have it sorted soon . I'm over in UK soon for work might catch up with there classic racing scene
Cheers Howard
Great to get it running ! I think you might need to look at the exhaust system . There might not be enough back pressure . Two Strokes are very fussy when it comes to exhausts.
yes my thoughts as well a pair of two into ones perhaps.
Totally agree!
My first thought too: They are dependant on the expansion chamber to draw the fuel mixture into the cylinder as well as drawing out the exhaust. The position of the chamber from the port is critical too, along with the timing of the closing of the intake over the exhaust ports.
My thought as well. I would suggest trying it with four seperate pipes to start with, and if that shows improvement, then start playing with tuning the lengths etc.
I was just about to make the same suggestion.
I chime in with another exhaust comment, as a rider of over 40 years. An expansion chamber exhaust is worth a try. There have to be many web plans for same; it could well cure the chuffing back through the carb.
A great video. Looking forward to seeing more about this but everything that you publish I'm going to watch. It's great to watch Old Masters at work
Perhaps a diaphragm carburetor would be better for running a two stroke engine, It would be better for fuel delivery i believe, as always your program is intellectually stimulating, thanks for the unique projects, i am a weird engine fan for a lifetime,👍
I've had a similar problem with a soviet chainsaw engine from 1976, where it would backfire through the carburetor.
The problem turned out to be the piston. It was a standard aluminum piston but the ring retainers were made of brass and were riveted through the piston into the ring grooves.
Over time the retainer loosened up and allowed combustion gasses to go through the ring groove and under the piston, which would cause it to backfire.
The fix was quite easy, i just made a tool to get into the piston and behind the ring retainer to peen it over some more and that fixed all of my problems.
Impressive you have be able to achieve as much as you have. More impressive was that you got up from your knees! So glad the videos keep coming.
If you need help with the engine , perhaps if that lovely Mr Millyard is watching this he could offer some advice . A collaboration between you two is something I'd pay you tube to watch . Keep up the good work .
Yes, Allen Millyard's name immediately popped into my head also.
Wonderful job getting it running. Definitely the right idea to put it aside for a bit and work on it again with a clear head.
I remeber years ago putting the cylinder head on the wrong way around on a CZ or MZ and it gave me the same issues of spitting back, it looks like the bolt pattern may allow this on this engine. Hope you continue to pursue it and get this one to run properly.
Yes it looks like the spark plugs are on the far side of the heads when Ivan first showed it before the rebuild.
The heads are on backwards. The spark plugs go to the rear , over top of the intake cylinders. The engine is also turning backwards. These engines rotate counter clockwise. Clockwise rotation causes the intake ports to open far too early and the exhaust opens late. The ignition timing will also be off if it was set for clockwise rotation.
Super cool engine. I hope it gets sorted.
Cheers
Fred
It is good to hear you have a new camera person on staff now. I am sure with time, you will get that rather bizarre engine sorted. It is good to see you back online. You always have the coolest stuff.
I wouldn't say this is the case here, but that engine sounds as if it is over oiled, running with an "almost missfire" at a large throttle opening. Spluttering (or 4 stroking) we called it 45 years ago; on my Yamaha 50cc it was easily cured by adjusting the autolube pump. Also sometimes caused by over rich mixture, which could point to your carb...
I think it is important that the pistons are in the correct cylinders, two are slightly longer than the others, if they are visa versa they will push the charge back into the previous cylinder instead of the exhaust.
It was 1971 when I last worked on a Puck split single and the memory is a little vague.
Well done Ivan and John! Keep em coming:-)
No background music while your talking please, some of us deaf old gits find it hard to hear with background noise.
Other than that, love seeing what you are up too again.
Thank you for helping us make videos better. In the following videos, no music during the call.
@@ТатьянаМанек-с3ч Thanks for your amazingly fast unexpected response, keep up the good work & I hope you are enjoying the shed work.
Hi , I have had experience with outboard motor ( two stroke) that commonly spat back through the carb ,this was caused by a lean mixture at low speed, the spit Back stopped when engine was under load , try putting a load on the engine. Roger in Norfolk.
From what I can see in your video the exhaust is a straight through pipe with no expansion chamber 🤔 in my experience all 2strokes need the expansion chamber to create back pressure and I think that this will make the engine run better also 🤔🤘 I've not seen one of these engines but have worked on 2strokes all my life , from motorbikes to outboard engines from 2hp to 250hp 😉 good luck with the build 🤘
great content guys! Nice double piston puch like engine. Looks like the intake timing is way to high, so maybe the crank is wrong way mounted? exhaust piston is now the intake piston viceverse?
Two stroke engines the INTAKE goes thru the crankcase NOT the cylinder head like normal engines! 👍👍 The two stroke sounded like MAYBE the sparks were out of time ( i could be completely wrong ).
I would look closely at the ignition system for A. possible bad condensers out of the box (seen that more than once) B. too much voltage to the coil(s) causing the points to arc (install ballast resistor). I would also look into maybe turning the heads around with the plugs on the opposite side. It looks like they'll go on either way from what I saw with the bolt pattern. If the plugs are over the intake side, it's possible they're firing before the ports are fully closed and causing the backfire through the carb. (Overvolting the coils will give a similar condition though). Just a few ideas.😉
With your 4 stroke 2 cylinder engine, I think it would have been better if the crankshaft was made so the both pistons were at the top at the same time. This is because it takes 720° of rotation for each cycle and the second cylinder should be firing 360° after the first cylinder... with this crankshaft set up you have created, the second cylinder is only 180° after. Just my thoughts... fascinating videos 👍🏻
I don't know how, but you are setting fire to the 2T mix in the crankcase. You can see all the soot in the bottom crank case halve. It looks like some sort of ignition misfire happening when the inlet ports are open and flashing right down through the entire crank case. Is there a chance the ignition coils are interfering with each other ? As a test completely separate the ignitions so they are like two completely separate motors. the only common thing is the points cam. The wires to the coils 2-3 inches apart, the coils a foot apart etc. Also mark the crank pulley for tdc for each piston pair. Start the motor. Then put timing light on each plug lead and check the ignition is happening correctly on each pot and keeps doing so as you bring the rpm up. 2nd also check the opposing cyclinder isnt being fired at bottom dead center by EMF or something weird. 3ndly 70's 2T motor cycles didn't run any mechanical ignition advance. I'd disable any advance mechanisms. Then using a dial indicator have the points close about 3mm before top dead center btdc. 5th Also is it possible the exhaust merge pipe is setting fire to the opposing cylinder , while the exhaust port is open and the un-scavenged 2T mix is wofting out of the cylinder. Maybe seperate the left and right pipes. 6th Also, 2 strokes can run forward or backward , they don't care much (a back fire can result in motor running backward and they keep running until the kill switch is pressed). That crank seal direction won't matter, the tiniest bit of air it might suck is not going to cause this issue. good luck.
I just read more comments, so I was beating to the punch on the exhaust being wrong 😑 Anyway good luck 🍀👍🏻
Are the cylinder liners removable or is it all part of the barrel? Just wondered if a transfer port or something is at the wrong height? Are the piston heights the same or is one taller than the other? You mentioned the reed valve being swapped out and not making a difference but surely if the reeds were closing properly it would be impossible for it to back fire through the carb?
I’m no 2 stroke expert, just throwing ideas at it in case one of them helps find a solution.
Great Chanel guys. Love your work and really appreciate you taking the time to share it with us.
I think mostly induction. Maybe crankcase pressure overcoming the reeds? Transfer port timing?
Problem is it could be a combination of things, but it shouldn't be able to blow back through the carburettor..
This is the best on UA-cam. That simple.
6:49 Ivan kicks the recalcitrant two-stroke....
Have you considered fitting a carburettor as fitted to the bike engine it's based on?
How about a carb from a Kart
maybe there there is to much airflow in the exhaust, could try and put a temporary restrictor to restrict the airflow of the exhaust.
Great videos keep it up.
My 10 cents worth is that with the combined exhaust the flame from from cylinder "B" is travelling out the pipe and a bit of it travels back down the pipe of cylinder "A" (when cylinder "A"s') transfer ports are open. Thereby igniting the air/fuel right back through the system. Ken Brough
Most two stroke engines need a little back pressure via an expansion chamber (exhaust) to even run , the down side to this is the exhaust will need to be tuned to the engine and maybe custom made if the engine isnt stock..
Not sure if it's been suggested but have you contacted Sammy Miller in the New Forest, he's got an amazing variety of weird and wonderful stuff including split single (ok yours is a split twin) strokers.
Glad you found the comments useful, I am sure most of us meant them in the nicest way. The engine is a puzzle as it is not conventional. Chuffing out of the intake does suggest that something about the timing is marginal but I had another random thought, are you setting it for the wrong piston? IE before the wrong TDC? Presumably the ignition timing should be just ahead of the second piston? I know nothing about these engines, it did sound good on song but the chuffing suggest it is firing far too early before the intake transfer port is closed.
Another possibility is a plugged exhaust or exhaust port- both are somewhat "normal" problems to have on older two strokes. Notice that the engine doesnt begin popping out the carb right away, but then when it does, it looks like exhaust.
Right then Mr. Dutton. That certainly appears to be two SG 250 Puch Twingles lashed together. I reckon you want to get your hands on one of those and do a comparison as to port timing, perhaps they mucked with that when they built up this prototype (although I suspect the cylinder liners are simply stock Puch liners). As well, your carburettor is completely crap, not even in the ballpark mixturewise. I'd have a hunt for two carbs off an SG and be done with it. Tell you what though, even two SG250 engines won't pull the skin off a rice pudding. The bike would do perhaps 70 mph (nah it wouldn't) if you wrung its fookin neck and laid down like Rollie Free. I personally don't believe the oil seal orientation made any difference. Two stroke crankshaft seals are somewhat special as they are engineered to contain pressure and prevent vacuum leakage. If you're using plain old seals you really want two slim seals installed back to back. That'll do the trick and I have actually done this. Are you ABSOLUTELY certain it is turning the correct direction? Virtually all two strokes will run backwards, just not very well, although that's mostly to do with ignition timing. not the reversed rotation per se.
"It's been a bloody nightmare"
Possibly why it didn't make it past the concept and development stage? Took too long to get working and running well enough to make it to the next stage - especially with working four stroke designs in competition.
Great stuff. No need for the music though, as I can't hear what Ivan is saying. Keep up the good work!
I've been enjoying your endeavours with odd engines. Good clean fun! Keep it up please. Just one little complaint though, regarding the cliche that petrol heads all like heavy rock and electric guitar. I'm certainly one who doesn't, and was most glad when it finished. Cheers.
I turned it up louder.... and Liked and Subbed..! lol.!
Hello again. As I mentioned before, it is going to be the correct mixture in the engine that matters. About 40 years ago a friend and I built a single cylinder scooter engine. We fitted a very expensive Fish injector. When it arrived the injector turned out to be just a big bore vertical tube with a simple butterfly and a, specific bore, sideways tube (jet) to supply the fuel. No float chamber. The fuel was delivered by gravity and had to be turned on and off by the tank tap. If you forgot the engine filled with fuel! This did give a large increase in power. Obviously the quality of the carburettion was not important - just the amount of fuel! The porting in the engine, which presumably has not changed, is fixed so that only leaves the exhaust which would usually be of an expansion/extractor type which would help pull the exhaust out and the new mixture through. These tuned exhausts are/were a bit of a dark art. My father in law was a kart builder and racer of some success who built his exhausts by trial and error - I think. His engines were just single cylinder Villiers 9E's with larger Amal carb. with the porting tuned as well. It might be worth trying your engine without the exhaust pipe to see if there is a difference. Good luck
Is that two stroke engine from a Rough Superior.. lol
Great to see you back in the swing of things..
I'd say your exhaust is the cause of the spit back through the carb. With that collector you'll get a real hard pressure pulse back at the port.
Hi, the backfire through carb could be poor seal between the two crankcases in the middle of the crank allowing pressure to come back through carb. You may need two seals back to back to stop this happening.
bing a 2 stroke it needs an expansion chamber on the exhaust to get the right backpressure.. the way its spluttering indicates the backpressure builds too much until it pops out the inlet, get a 2T exhaust system off a motorbike anf try that im sure it will massively improve things ..Love this chanel BTW and the things you all do :)
I wonder if your middle crank seal is leaking letting the compression and drawing vaccume between the two bottom ends transfer. It doesn't look like there is a rubber seal in there , I have seen snowmobile engines with a labyrinth seal between the two sides of a crankshaft but I don't see that in yours either...
Hugs from Canada
well done Ivan , John and a big thanks to the new video production person cracking job , looking forward to the next instalment , ps i have always had a love hate relationship with any thing 2 stroke they either work real well or just a complete nightmare
Have you tried an exhaust with an expansion chamber? This will cause the exhaust pulse to help pull in the incoming charge and keep it from blowing back through the carb. Just a wild thought....?????
A normal 2 stroke engine can run in either direction, all that changes is the ignition timing. A twingle is different since the exhaust and transfer ports are in different barrels. That means that it is possible to have the transfer ports opening before the exhaust if the engine is running backwards. The result would be blowing back through the carburettor. I would have another look at that before dismissing it completely.
Alternatively, is it possible that the barrels are reversed? I'm unsure if the primary con rod is on the transfer side or the exhaust side but if they are the wrong way round it would throw the timing out completely.
Exactly my thoughts, too. Also i noted that the exhaust pipes doesn’t look like they offer back pressure of any kind. The design of the transfer ports could also be relying on this back pressure so maybe also a potential culpritt ?
Racing Scotts had straight pipes with no issues, indeed ran worse with expansion chambers, also many Aero engines. Maybe induction is the issue? Is it reed, rotary valve or piston ported?
Got to agree with a lot of other comments re exhaust I’m sure an expansion pipe would help , I used to have the formula for working out the cones somewhere
it implies from the flow that's it's backwards it should never be able to have exhaust smoke from the carb as there should be a piston in the way or the ports should be shut. are the pistons " handed" ?
Suggestion: use the carb off a Rotax two stroke engine. They fit to the manifold byway of a Felix pipe and jubilee clip. The miss fire appears to be something to do with the timing. One cylinder might be out of phase. Best of luck. Graham P.
How are the points cam timed? Did someone pull the cam off to replace crank bearings & get it back on wrong. Some 2 strokes don't use a key way for alignment of the points cam. If that's the case good luck on checking & correcting.
I'm pretty sure it needs separate exhaust pipes, as suggested below. Never seen a multi-cylinder two-stroke with a common exhaust system. One cylinder opens the exhaust port on the Powerstroke while the other is closing it during the intake stroke, and then there is an open connection to the carb causing the backfire. The easy way to test is to remove the exhaust pipe and start it up.
Two stroke cars do, but design will be critical. You want it to push back enough to stop the fuel air charge escaping out the exhaust but not enough to backfire like this! One for the maths wizards I think.
Could do 3 separate expansion chambers, each with reed valves where they join to one common pipe? I wonder if that'd work
Also on the Puch175 and 250 the spark plug is over the transfer piston.
2 stroke expansion chamber exhaust science . it will take you a long time to get the shape and length right . good luck old boy . from nassau long island usa
Cheers for the update. Life is fun? 🙂
I had a Puch 175, not a fussy engine it ran 24:1 on sae 30 with worn pistons.The misfire sounds like ignition. Two other possibilities, maybe it needs 2 carbs? no one ever made a double twingle afaik. secondly could the compression be too high? love the channel, it's all real.
I have a love/hate relationship with 2-strokes, they're wonderfully simple and can run and sound fantastic when things are going well, but they're finicky, high-maintainence little beasts! apart from very early examples (full of cast iron and bronze-bushes) they've got a limited lifespan too!
I reckon the backfiring could be down to the exhaust, most 2-strokes rely heavily on the resonance of the pipe to run, and keep the gasses moving in the correct direction. although older 2-strokes (pre-war especially) are quite happy without a resonating pipe I think if you made something up along the same lines as was fitted to the puch bike engines, you'd at least eliminate that issue.
Iirc 29 inch pipe length for individual pipes from the piston should give the right reversion pulses from an open ended pipe.... the reflected pulse should arrive back at the right time..
I've seen Suzuki Water Bottles with bloody light years on them running merrily along. 70,000 - 80,000 miles was not particularly remarkable if you kept oil in the injection tank. Certainly I've seen regularly used outboard motor two strokes that were 50 years old and had never been to bits.
@@scheusselmensch5713 It all depends on the care taken when operating i suppose, most of the 2-strokes I see are thrashed within an inch of their life and only get attention when they won't thrash any more! there's plenty of them out there that have a LOT of hours on them and are still ticking, but the vast majority tend to live fast and die young. I'll still stick to the old iron though, it smells of castrol and makes better noises!
@@theafro life of a 2 stroke all comes down to feeding and maintenance. Use proper fuels and oil warm them up properly and provide the proper maintenance when required and they will run forever
@@holmes1956O the trouble is, that the majority of 2-stroke users nowadays are either young lads on scooters or arborists with chainsaws/brush-cutters, neither category are known for mechanical sympathy!
The engine design is pre WW2 . back then the racing DKW split singles ran on open megaphone exhausts , the post war EMC racers did the same, this engine is a pair of EMC built Puch design twingles so does not need expansion chambers. I ran my Puch 175 with the exhaust internals removed (open megaphone) the noise was incredible!! but it ran fine. I put another Puch engine in a home made scrambler with a 2 into 1 exhaust ending into an old car silencer !! that ran great too. This was back in the mid 1970's LOL
It seems as if the exhaust is not scavenging properly. It needs an expansion chamber, or scavenger pipes to clear the cylinders better
Thanks for all the very interesting content.
I'd be inclined to try an expansion chamber type exhaust on it, I don't know a huge lot about 2 strokes but somebody did tell me once that "the exhaust is half the engine" with them.
To all the folks in here saying it needs a proper exhaust, you are both right and wrong. I have been around the good old 2 stroke engine in snowmobiles and motorcycles for about 40 years now. For best performance at a given rpm yes a tunned pipe is needed bit just to run on a stand they should run just fine even without a manifold. Will they have power? Probably not a lot but will still idle and rev just fine.
My thoughts on this engine is ignition or port timing is off, most likely ignition. Someone mentioned spark plugs and I certainly would start there.
On some of my 2 strokes I found playing with spark plugs improved thing alarmingly and playing with the exhaust design ,if you can remember the Arial Arrow it went like a rocket with what we called crackle pipes fitted which altered the flow of air through the cylinders
It maybe an idea to talk to Villier go kart owners as they had the art of exhausts off to a tee ,the 9E bottom end was the engine that took a few titles in its time
I want to weld up four massive expansion chambers for that engine, should help a bunch!
I suggest trying slightly earlier ignition timing, and also sparking plugs with precious metal electrode tips. I think the combustion is taking place too late and/or too slowly, so it is not completed by the time the transfer ports open. I suspect that this design of engine may need more ignition advance than a conventional engine, because the flame has further to go from the sparking plug to the far sides of the cylinders. Also regarding the direction of rotation, the split layout gives asymmetric timing of the transfer and exhaust ports and this has to be in the right direction. If you imagine the engine in a motorcycle then if it is turning in the same direction as the wheels the transfer ports need to be on the front cylinders and the exhaust ports on the rear cylinders; vice versa if the engine runs in the opposite direction to the wheels. If the engine is running in the wrong direction, the transfer ports are possibly opening before the exhaust ports; I think this would cause a strong tendency to spit back.
Further to my previous comment, I think it is possible to see from the video that the positions of the transfer and exhaust ports are correct for the direction of rotation, assuming that it is clockwise as seen from the end with the ignition system.
Yet another thought: what is the definition of top dead centre on a "split" engine? There is a point of maximum compression, at which the piston on the exhaust side is already on the way down and the piston on the transfer side has not yet reached the top of its stroke. I think this point of maximum compression has to be regarded as top dead centre for the purpose of determining suitable ignition timing. You could find it accurately with a U-shaped transparent tube with some oil in it, attached at one end to a bung that fits into one of the sparking plug holes.
excellent video, interesting problem ,for the exhaust smoke to come out the carb the pistons and ports need to be open on both cylinders and that would happen, I'm assuming a intake piston and a exhaust piston with a shared combustion chamber, it looks like you are either missing a valve on the intake or ....you have an open intake it couldn't be that there is supposed to be an air filter or intake pipework so the moving air mass is involved in the scavenging, at what point does the plug fire? and is it a wasted spark system with the wasted spark igniting the remains of an over rich combustion event ? I would stick a scope on the timing to be honest it's so close
Are your primary pipes from the cylinder to the collector box too short causing exhaust gases from one cylinder to "short circuit" into the other cylinder causing the misfire as it looked in the video like the exhaust pipe would shake when the misfire occurred, also the collector box for the primaries looked very small which could be exacerbating the problem as the exhaust is remaining "pressurised" from one cylinders exhaust event to the next cylinders.
I've been doing a lot of thinking about your 2 stroke backfiring through the carb. You need to get rid of your wasted spark on the exhaust stroke. What is happening is the fuel is firing before the piston passes the port. This thought came to me in a dream around 4 am in the morning and I woke up and I'm sitting texting you on my phone in CoArmagh were I live before I forget. Please let me / us know how you get on with this theory / dream. Regards Alan Winter
As many others have suggested, get a good exhausts made with a suitable expansion box/chambers and separate the exhausts
Maybe the long and short pistons are swapped?
I agree with the others that the 2 stroke engine needs 4 individual pipes
Are the pistons in the correct cylinders? 🤷🏿♂️
This has been a fascinating series. I have yet to understand how that 2-cycle arrangement works with the paired pistons. :-/
Basicly one piston controls the intake function and the other controls the exhaust. This allows the port timing to be asimetrical so you can favor port opening and closing for best power . Normal single piston 2 stroke port timing is always a compromise , porting for max power usually kills the bottom end. Reed valves or rotory valves on the intake and tuned exhaust are ways improve the power band while still trying to obtain max power with a usuable power band.
@@dog8nut Ah, got it. Thanks! I see they share a common combustion chamber, so it makes sense now.
@@dog8nut I don't think so as surely you would only have 2 exhaust ports for your arrangement.
I think we simply have a 4 cylinder 2 stroke, arranged like a v4 or parallel 4
@@psk5746 The orignal PUCH design used twin exhaust ports on their 2 piston ONE COMBUSTION CHAMBER engine. So what we have in this case is a 2 cylinder 4 piston parllel twin with 2 combustion chambers. Still with 2 exhaust ports/pipes per cylinder.