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Understanding the Parts of a Motorcycle Carburetor | MC Garage
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- Опубліковано 17 сер 2024
- The first part of tuning a motorcycle carburetor is understanding what each part does. What does a pilot jet do in a carburetor? What about a needle jet? How does the choke work? This episode of MC Garage covers the major parts of a motorcycle carburetor.
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Modern fuel injection is amazing, but before injectors, ECUs, and fuel pumps motorcycles used carburetors. Some smaller bikes and two-strokes still do. Today on MC Garage we talk about the carburetor.
For those of you who have an older motorcycle model or a modern two-stroke, one of the most confusing and intimidating tasks is probably jetting the carburetor correctly. To some, it amounts to black magic. But if you know the theory and reasons for each circuit in your Mikuni, Keihin, or Lectron and you take it step by step, it’s really not too difficult. Today we are going to start a multipart series on how to tune or “jet” a carb. Step one is to understand how it works and what all the parts do.
So how does the carb mix that fuel and air? In simplest terms the air comes through the venturi and mixes with fuel supplied by the carb in a specific ratio. This is called the stoichiometric ratio. That ratio is theoretically 14.7 parts air to one part fuel. In reality, your machine probably runs better at a richer ratio. Some tuners say 13.2, some say 13.7-each motorcycle has its own happy ratio for proper combustion. This mixture is achieved using small orifices or jets to mix the fuel with the air.
First and foremost, there is the place the fuel is pulled from: the float bowl. The float sets the level of the fuel from which the jets pull. The float operates the needle valve, letting fuel flow in when the level drops and closes when the correct level is reached.
On the bottom for the carburetor you typically have two jets. The pilot, the smaller of the two, and the main jet. Let’s start with the pilot. The pilot jet handles the mixture from idle to 15 to 20 percent throttle. Air comes in through the front of the carburetor drawing fuel up through the pilot with a vacuum that is created as the air flows through the pilot circuit.
When your engine is cold, a richer idle mixture is needed to make starting and running easier. This is the job of the choke. It adds more fuel into the mix to assist the idle circuit or pilot when the plunger is moved to open an additional path for that extra fuel. Once the engine is working, closing the circuit returns the carburetor to normal operation, relying only on the pilot for fuel.
On the side of the carb you have the mixture screw. Generally, if the screw is located on the engine side of the slide or butterfly, it is a fuel screw. Or if the screw is located on the airbox side of the slide, it’s an air mixture screw. Here you can fine-tune the idle and compensate for moderate changes in temperature and altitude without changing the pilot jet.
The larger jet next to the pilot is the main jet. This is screwed into the needle jet, sometimes this is referred to as the nozzle. More on the needle jet later. The main jet provides the fuel at 80 percent to wide-open throttle. The fuel flows up and out through the needle jet into the throat of the carburetor. When changes in air density are significant the main jet will need to be swapped.
Handling the mixture between the pilot and main is the needle jet and needle. This is your midrange, or about 20 percent to 80 percent throttle. Within the needle jet the needle moves up and down to vary the orifice size to meter the fuel. The tapered shape of the needle controls the amount of fuel coming up through the main jet and through the needle jet. As it goes up, the opening gets larger, letting more fuel into the mix. You can tune this function by moving the static position of the needle up or down or by changing the taper of the needle.
The needle sits in the slide that moves up and down with throttle position. That can be controlled by a cable the flat-slide we are using for this video or by airflow passing around the throttle butterfly on a CV, or constant velocity carb. In CV, a vacuum is created that sucks the slide up as airflow increases.
Those are the most important pieces of a carb and what they do. On the next episode we cover the tuning the idle circuit.
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You are single-handedly saving so many cafe racer projects with this series 😂
Modustollens1 I’m restoring a motorcycle myself, looking forward to this series
Modustollens1 Yamaha SR250, it has 99 000km or 65300 miles on it. Used to be a delivery bike and got it for $260. Its running okay (can do with a cleaned air filter and carb), but it requires a lot of cosmetic work and some frame repair (stand literally broke off the other day 😂)
Modustollens1 There is a lot of potential in that bike 👌🏼 Restoration or restoration and modifications?
Oh my god me
'what's a cafe racer?' hahahahaha *runs away*
Thanks for keeping MC Garage alive. Hoping for many more videos to come. 👍
Keep 'em comin'!! I was worried, but you guys are finding your way! That last group video was fun - tapped into that joy of riding the way those previous hosts used to.
I’m digging this series. Can’t wait to learn more
Thank you Sir for such a clear refresher lesson. You really are a good teacher!
Nice - thanks!. If you could spring for a few diagrams (cross sections etc.) that would help too (rookies like me anyway)
Nice video. I'd like to see more camera time on the actual carburetor so we can see the parts and their relation to each other; less on the presenter. +1 on an earlier comment requesting diagrams. Or animation.
Animated explanations would be more helpful....I don't know how u guys manage to read my mind, every time I had doubt, u guys come with the related video.
Love from India.
I'm glad you're tackling this stuff. But...
I thought you went too fast and covered way too much for an intro. I doubt anyone who doesn't already know how carbs work was able to follow well. Also, the camera angles were too haphazard. I think some diagrams would have helped a lot.
My thoughts pretty much to a tee. ^^^ No time to ponder anything and sort it in my head as you go. Too fast for people who are already drowning in a sea of new info and ideas.
You didn't "dumb it down," but you didn't make it impossible to understand the basics. Great work!
Timely, just ordered an Eagle Mike, KLX jet kit, carb screw upgrade, manual petcock for my KLR650.
I'm a fan of most things related to motorcycles. Here are a few suggested topics for future videos. Measuring spokes and relacing wheels. Troubleshooting ignition problems. Hydraulic clutch. Charging systems. Thanks for video!
as i said, great. and i never knew about chokes that didn't have a butterfly to 'choke' the air supply but just had a plunger to enrich fuel. every day is a lesson! love your page.
I just got an old suzuki tempter. Its my first bike and im learning how to work on it. So far its been an enjoyable nightmare... On the internet Its like they never existed......lol
Anyway ur videos are an incredible resource thank you. They are damn perfect no cheesy jokes no arrogance perfect....thanks so much
Better than expected. I thought I knew a fair amount about carburetors, and I've learned something already. Hopefully at some point you will also explain that they seem to be on the way out due to European emission standards, which has sparked the innovation of fuel injection for 2-strokes. Keep up the great work!
How have I been watching since the days of Ari Henning and only now subscribed. This! This is what I've always needed! how a carburetor works.
I tried cleaning mine one time on my DRZ400 and I was so proud of myself for managing to put everything back together but as soon as I turned on the bike. It would choke at 1/4 throttle. So I just gave up and gave it to a shop hopefully this series will teach me once and for all how to be self-sufficient
Great job, just funny: I ordered a racing carb for my go cart thingking it would be like the stock carb or a car carb. I have never seen a bike carb before, unfortunately. At first, I thought something was missing. Maybe one day I'll be fortunate enough to have a bike to work on. Thank you. Thumbs up and like this guy. 👍
Welcome Justin. First MC garage video I’ve watched since the Ari era. Thanks for continuing this series. Watched all of Ari’s stuff.
Thank you for keeping MC Garage alive !!! Hope to see lots of interesting videos in the future
Ironically just switched from f.i. to carb'd bike, these vids are much appreciated!
hehe same here. What bike did you get?
@@MrTn0099 A little orange smoker : ) You?
You know it is a good video when the "most replayed" graph arcs over the whole video.
This is a great video. It's nuts how much info you gave in such a short video. Def saving hella projects with this info
Well finally some actual mechanic work from this guy!
Nice Video. Remembers me to the old days when I started with a 50cc 2-stroke Yamaha and all the way up to the older 4 Strokes which were loaded by a carburator. Tuning it was a day to day job to keep the bike running! - Looking forward watching the next part of the series...
You have some big shoes to fill, man. Godspeed.
Amazing piece of art !! That we overlook this by seeing the ENGINE 😐
stumbled upon a video about carbs...and that's my bike! Nice.
Can you also tell about the common issues that an old carburettor may elicit? Or just some issues that comes with wrong settings or blocked jets. And how these issues can be solved?
I Wish I Had a Dad like This
Nice, good stuff! In 2 strokes carburetion is like the most important thing.
This could not have been posted at a better time, I`m looking at a gsx750F, and I need moar knowledge! Thanks! Also, done, done, and done!
Glad to see MC Garage is still moving forward after Kevin left. Keven was great and expect the same from new MC.
can't wait for the next episode. So want to learn more about it. Want to Tune up the CV Carb on my bike.
Great Series! Keep up the good work.
I'm excited! Can't wait! Thank you!
The best carb video I've ever seen! Very informative for a newbie like me
The fuel and air mix in the emulsion tubes. Some times the jet also has the emulsion tube, such as the idle/pilot jets, but most main circuits and secondaries do not.
I see so many of these. One single carb work. When doing 4 like on older motorcycles there are no videos. I would love to see a video on separation and then putting them back together. Especially on how to put the springs for the butterfly back in. I want to see if there is a different and easier way to do it as opposed to how I do it.
The more help we can all get with carbs, the better!
@adamwaheed , now we need Favourites & Fail episodes to continue in this platform 🤗
Hi, i cant find choke on my carburetor and my motorcycle usually run on high rpm while on idle. What should I do?
That bike is cleaner than my 19 years life-time Tho XD
Perfect, coming back in a month before I (attempt to) clean my carb.
The idle circuit is always the biggest problem and the hardest circuit to clean. You don't just clean the jets, you have to clean out the paths that lead away from the jet. You want to see a nice stream of carb clean coming out of the transition ports (tiny holes right next to the engine-side edge of the throttle plate/slide, can be up to 4 of them). If you don't achieve that, it won't run right. If it is a CV carb, be really really careful with the diaphragms. It has to seal 100% in the groove, or not only will it not run right, it will destroy the diaphragm. Good luck.
Thanks that was awesome! If only I knew that 20 years ago! But really good job explaining. Maybe you can do another one on FI?
I lost the small washer at the air mixture.can i replace it with umprovises one?
Other than the fuel and overflow hose, what are the other hoses and where do they connect to?
great series
well done beardy guy. tks
could you also talk about the tubes coming from and going to the carb?
I bought a bike that won't run and it has two tubes coming out of the carb. One to the fuel tank and one is clamped shut after about 4 centimeters. I don't know what it is/was and what it's function is supposed to be.
It is ridiculous, how complicated this shit is, anyone else :D?
Excellent videos, thank you.
Really nicely explained !
May ask you something?what carburater diameter size for get 50 cmf airflow?
Muy buen video 👏🏽👏🏽
Saludos🇦🇷
What is the proper float adjustment for a vm34 carb?
What is the jet that unscrews on the face of the carb and the small holes around the same area. 1980 yamaha xs 1100
awesome man
keep the great work up
Very nice video
I really like what you people are doing ..👌👌👌
Carburetors reigns
How does the jet needle not effect the first 20 percent of throttle? Needle jet starts opening with any throttle movement.
What are the tubes present outside
Awesome, this is exactly what i need
Anything coming up as regards flat slides vs. round slides? As one of my bikes is a antique of sorts ('73 Yamaha TX500, I'm the original owner) I've had to learn a bit about carb tuning in the past to get the mixture right for the aftermarket exhaust. It originally had Keihin CV's, I threw those out years ago in favor of round-slide Mikunis, which I bought from Gary Nixon back when he had a shop up in Cockeysville, MD. My Bonnie has Keihin CV's, wondering what advantages there might be to flat-slides that are available for it.
@Justin Dawes looking forward to getting my the CV carbs on my GS500E explained to me, they really seem like an overly complicated design for no real benefit to me but im sure there is some reason for it. A good explenation might make people with this bike stop turning their idle up to 5k rpm just because the bike wont start and run without the choke on for the first 15 or so minutes
hi, what carb should i use on my honda mtx ot running a 53mm piston and cylinder kit i have a 18mm carb on it but its pissing out petrol from the overflow an air filter an the bike dies when u drive it at high rpm like 9000 1000 rpm or goin flat out in 4th
Hey I have a motoku carb any idea if I need more than just the gas hose on it I'm pretty sure I have to re her it but my bike will start then die out like it's getting flooded
Can a flat slide carburetors be tuned for a 4 stroke engine? Does a carburetor's design dictate the type of engine that it is used for? I've never seen a CV carb on a 2 stroke. What are the different applications of a round slide, flat slide, and a CV? I would think that a carburetor 's function is to mix fuel and air to a specific ratio, so how it accomplishes that should be irrelevant to the operation of the engine.
Hey bro my motorcycle secondary trottle no move when I give gas stall ... a spring I think Brock ..
Hopefully there will be sufficient attention for 2 strokes and possibly oil mixture systems.
Hi guys I am restoring my 2009 Honda C100 and Ive recently upgraded the bore to 53mm from the stock 49mm. I am using the honda wave/innova 125 carburettor on this bike. Since I am just starting out and i dont have much knowledge in motorcycle/car engine modification, can you guys comment below and share some tips with me for a beginner like me to quickly pick up on? I am planning on replacing the standard spark plug coil that came with my bike with a thicker wire type. please do share some tips with me below?
Carbs all day. In a apocalyptic scenario who's gonna fix that FI? Carbs will still be around.
The warlords will all be fuel injection master technicians, obviously....
How can I reduce fuel consumption on my sanili motto circle?.
great tutorial, but why the pink fuel pipes? i thought only cheap chinese copy carbs had them?
Great video ; thanks
*Although I prefer FI, there’s something about pulling that choke lever in the morning and waiting for it to warm up*
great video
Great video👌
How often do you clean a carburetor in a year?
Video is really good good work
is it possible that the air screw influences the performance at 100% throttle as well? when i close or open it a bit, i feel like my scooter performs different. i have a 50cc scooter (Switzerland..) with a 12mm carb. and i have to drive it nearly always at full throttle.
what means feel different(clarify problem)? Full throttle because its fuck.ng 50cc ....
Please make a video about duolever front suspension
My idle is good and my WOT is good, and now to figure out part throttle.
how is that all the working parts of a carb what about accelerator pump and emulsion tube and the coasting enricher
What are all those pipes coming out of it
Great video, but would have really liked some kind of practical example, hopefully in the followup :D
Thank you.
Cool !
It was a good video
Carburetors... the best thing in life witch I will never understand fully.
1st out of 5 carb vids
Shouldn't the first adjustment to make or check when rebuilding a carb is the float level???
If the float level is off things can get difficult.
Incredible video Justin, I actually managed to expand my knowledge a little with this.... Never knew about the mixture screw actually being different depending on its location... Always thought it was fuel only.
Also, is it true what my father said where rejetting a 4 stroke can lead to damage or is he just trying to stop me tuning my bike? It's a 102cc scooter and factory has 7BHP. He gets to 65mph at a push right now so I'm hoping to get it to about 70-75mph tops by a small rejet of: from 85 on the main and 32 on the pilot, to about 100 main and 40 pilot with a pod air filter.... What's your advice on this?
Whats that open copper-looking pipe on the side of the carb???
@Justin Dawes I guess I'm educated enough about this to understand which one is for the fuel line. But the carb on my motorcycle also has this open copper-looking pipe on the "other side" of the fuel inlet. I've asked alot of people and they answer just like this. Not really the answer i was hoping for. And I don't think its a case of missing parts(pipe) It's been like that since it was bought.
Didn't even talk about all those pink tubes out of carbs. I have been searching what goes where but no where to be found. Except where gas tube goes, I have no idea of the rest.
Can i know the lateral function
Ty nice
I'm glad I cut carbs from my diet...
rof
Hi sir why the motorcycle can suddenly stop the engine
@mcgarage great video. Could you also cover how ECU maps work with carburetor and how custom maps improve things.
Hi beardie 🤩
i just want to check the next one. maybe put both approaches (one with proper tools, and one with DIY no tools)