Starting and Tuning a 4 cycle OS FS-91 Surpass
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- Опубліковано 5 лют 2025
- Ever wondered how to start and tune a 4 cycle Nitro RC Airplane Engine? Tune in as Tom shows the procedure he goes through to start his 4 cycle nitro engines, and how he properly tunes them after they're running.
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You definitely know how to tune a glow engine better than anyone else I've seen on UA-cam! Good information!
Thanks Tom, I have the OS 91 surpass. After being a victim of a glitchy radio it went in pretty hard. I don't know how damaged it really is. It doesn't look bad, but it's been sitting for 15 years. I want to revive it and put it on a U Can Do that has been almost ready to fly for about 12 years. LOL You can't rush these things. Your video is a good refresher for what I should already know, and I appreciate the contribution you're making to the hobby. I'll watch this video again after I put to engine on the stand. BTW I like your test stand.
This was very useful. Thanks a lot from Norway!
Absolute best tuning video on UA-cam, really fun and satisfying to run a four stroke great power plants for rc planes, shame people give up on them and use batteries so boring
This video couldn’t have come at a better time, Tom! I have an old FS-91 Surpass that I just restored to operation and it just so happens to be my first 4 stroke. Thanks!!
Excellent video! I just got my hands on a few nitro and gas planes. Some are 4 stroke, some are 2, and a couple are gas. I completely enjoy tinkering with them and the realism of flight vs. electric is unrivaled. Call me old school. :-)
Great video with good tips! Thanks for explaining the leaning/overheating aspect that too many pilots don’t always grasp. Remember, as the tanks fuel level decreases, this can sometimes cause the engine to lean, and run hotter, reinforcing the need to richen the top end needle before takeoff. Fuel is part of the fuel system, but is also part of the cooling system! You have a good technique on low end adjustment too! Thanks!
Exactly! MOST engines run leaner as the fuel level drops under about half a tank. I ALWAYS take this into consideration.
Great info. Ear tuning the 4 cycle is a goal of mine. I liked the info on the high and slow speed settings. Much more straight forward than the manuals!
Very informative. I’m looking forward to owning an OS91 soon.
Happy to discover and join this new channel for me !!! greetings from Italy ! please keep making videos ! :-)
I'm glad I found this, I have the same engine. I wanted to take the throttle arm off so I set about undoing that mixture screw. I wouldn't feel quite so stupid if it was the first time I'd done it but, no, I did it a few years ago to a Saito (I'm pretty sure it was a Saito). Back then I was the club beginner and other, wiser heads stepped in to fix it. Not so now, I have to work this out myself so, as I say, I'm glad I found this, thanks for posting it.
I watched your video because I have an OS FS70 (has run only 1 or so tankful, so new). I'm having difficulty keeping it running at low speed, so I'll try what you've just done on the .91. I'll let you know how it turns out. Thanks for taking the time to make this video.
Very good video and very well explained. I enjoyed watching this very much. Thanks for sharing.
Nice!!!! Thank you
In full scale, running lean of peak is acceptable. Temps actually decrease, due to less fuel burning. I don't use that procedure with my model engines though. As altitude increases, air is thinner, causing a richer mixture as you climb. In full scale, the mixture can be adjusted for this while flying...so slightly rich is better with the models.
I hope I can get mine running as smoothly as you got yours. 👍😎🤘
Nicely done video.
Interesting when you give it a gas we can see the fuel tank almost blowing out that's nice! please do you have any idea how can I figure out witch tubing size for each engine? tks
Superb video - clear and concise, thank you !
Very well done…learned lots
Great video and info! Your subject airplane looks like it has a very high wing loading
I am struggling with the low end adjustment to achieve the cackle. Could someone please prove the factory setting for the low end adjustment? Right now the engine dies when the glow plug is removed which makes me think it’s rich but when I lean it from there then it won’t start.
Thanks Tom 👍🛩️
First time I've watched a video on this channel. Really like Tom's approach to describing what he's doing. Tom, do you have a particular method for tuning four strokes when they are mounted inverted in models?
One of mine seems to be very reliant on an on board glow system in order to keep running at low speed.
Excellent video thanks for sharing
Very nice 👍
I didn't quite catch how you set the idle mixture - are you shooting for max idle RPM then enriching it a bit, like the top end? And then checking to make sure the engine doesn't die with throttle input, and enriching it a bit more?
Excellent thanks
My Magnum GP-40 2-Stroke ALWAYS starts in one try by bumping it backwards against compression, with the slightest effort, with the spinner cone between my 2 fingers. Easiest starting engine I've ever had...
Awesome!!! Love it. Bigger props will hurt you!!!
Sound of is amazing!!
Thanks!🙂
Interesting. Can you explain something to me? I am coming from a motor cycle engine background and I am wondering how well the bottom end is lubricated in these four stroke engines - the crank and the camshaft and followers, and how are the rockers and valve stems lubricated please? Is the oil passed down by 'blow by' enough, and if so, is there a possibility that too much oil can build in the crank case? What proportion of oil is included in the fuel? Thanks if you get time to address this issue.
Nice
Real doctor.
Hello, could you indicate the pitch and diameter of the propeller? Thank you.
I have a OS surpass 70 what is the high-speed needle setting for break-in
Looks so easy to do,,,
I have been struggling with a Saito FA170R3,, Very hard to find any "sweet spot".
4 stroke with glow plug, what fuel Do you use?
Where should the low speed needle be set on a surpass 70 as a starting point? How many turns out? Engine has been broken down and cleaned. Thanks.
Did I watch you prime it counter clockwise? Then start it clockwise?
Free advice, always use after run oil with 4 strokes
Hey Tom love you videos on the four strokers,I have a question on the fuel you use could you tell me if it is synthetic,caster,blended and what percentage of nitro do you run.thNks for your time.
Hi Tom great video thanks, I'm having a issue with my os- fs -91( same engine as video ) runs great at high end but stalls at idle. Any suggestions would be helpful thank you Dave
Hi.......what's the % of oil use to the fuel ?
Great vid. But what’s up with the lawn mower ? 😂 look behind him.
Great video Tom, I have a question do all the OS FS line of engines have a low speed idle mixture screw ? Thanks again I will
Be applying this to my set up schedule!
Really makes me wonder if lean of peak (on the high end) could work on this scale as well.
I don't have any experience with RC 4 strokes, and it's been a few years since I flicked a 2 stroke. I seem to remember if you tuned it lean of peak you'd risk stalling when advancing the throttle. What do you reckon?
Yep. That's also a good indicator of an engine that is running lean, but that can also be a symptom of a lean low speed needle. So, I always start with tuning them rich and working my way towards peak.
What happens if we set up the engine vertically?
I have an OS 95V 4-stroke and can't seem to get it running. It's mounted inverted in a Tiger Moth.
What is the barb on the bottom far?
Being a 4 stroke do they run on the fuel we put in our cars. Cars as in the ones we drive to the grocery store.
Just ask the same question...
@@BrianSmith-ug2bu Hi Brian, I didn't follow up with the fuel and sold my 4 stroke engine and have gone over to electric planes and gliders.
What I did find out is the 4 stroke is a special fuel with different oil ratios' depending on the engines and sizes.
Hi I’m John I’ve got a 2 stroke engine with a 2 blade propeller what should the top RPM please and could you recommend a good tachometer for me just starting out with a hanger 9 pulse 40 please regards John
Tom, my engine is pretty gummed after sitting for years. I'm building a test stand to get this same engine running again. If I were to take things apart to clean it up, what is a good starting point for the high and low speed needles? (How many turns from fully closed?) I assume that's the way to get started.
1.5 open on high, the low should be flush with the throttle arm body
what's the starting point (turns from closed) for the low speed screw? thanks!
With the O.S. carbs, if I can't find the manual online somewhere to get the manufacturer's recommended starting points, I'll start with low speed needle flush with the outside of it's bore, and I start with the high speed out about 4 turns from fully closed and gradually work it in as testing progresses.
@@RCPlaneLab thank you!
what fuel did you use there?
I am just getting started with glow 4-strokes and this is an excellent video to learn about setting it up correctly. Do you set up your engines on the stand before finally mounting them on a plane? Also, would you mind sharing and showing how you built the motor test stand? Thx a lot.
Hi, great video, thanks. I'm having some issues with my OS Engines 120 Surpass II.... I can't find the correct position of the idle mixing valve.... I've replaced the glow plug, have moved the valve back and forth to no avail. What is your best guesstimate on turns of his valve? Thanks
If you mean the low speed needle, I would start with the needle face being flush with the outer surface of the barrel. For example, if you looked at the needle from the side, the needle face should be in the same plane as the end of the throttle barrel. Hope that makes sense!
@@RCPlaneLab Thanks for the advice.... I tried many many times with frustration as a result.... by any chance, if you can of course, can you tell me in your specific engine, how many turns is your ideal setting of the low sped needle from fully closed position? It might help me better; thanks in advance
Whta prop you recommend
Hi i see you do not use eletric starter......good
Do you have any experience with this engine (actually the 2nd version of this OS 91) in a cowled airplane? My OS 91 FS-II would always start well and roar off the ground but when flying for a bit, it would seem "saggy". I progressively ran this richer and richer but it never solved the problem. Then, it was dead-sticks. Does anybody have any thoughts about this?
Hi Chris, I've run a few of these over the years in cowled installations. If I've ever had the problem you describe, I can't remember, lol. Here's something to consider though: when an engine is run on the ground, it never really gets a chance to 'unload'. Maybe as the engine 'unloads' in the air, and gets cooling air over the cylinder, it cools and richens further? Have you tried starting with a slightly leaner than optimal condition on the ground to see if it helps matters while in the air? I don't like running engines lean, but as a test it may be beneficial to see what effect it has.
sounds silly but probably not proper airflow at altitude .or pressure problem could cause fuel flow issue
Could be tank height to low as well
Nice. Nothin' like the sound of a little OS 4 stroke! That thing runs like a sewing machine.
Four-stroke glow engine nitro is only an additive.
2:52 khaby lame moment