I just want to say a massive thanks for this video. I dont think ive ever learnt so much in such a short period of time. I will be sure to buy all my mikuni gear through you guys from now on.
You have provided the best information for these carbs. I have been jetting for weeks! Midrange is still to lean in richest position on the needle. You mention go to the next size needle jet! Thank you!!!
Great information. I fitted a vm34 to my SR500 Yamaha yesterday. Much better than the original carb. After watching this I'm going to do what you've explained & I'm sure it'll get even better. Cheers from Great Britain
Love your work mate, learnt more in these few minutes, than I have reading about carbi tuning, I've found there is so much miss leading in formation out there, I would of liked your input on setting float tang setting and its affects too, with my YAMAHA AG100 1973 that uses a mikuni vm20, it's to be set at 19.2mm, from carbi side of bowl gasket, no gasket in place, to the highest point of float, when in the upside down position, without pushing needle spring in.
Very very informative. I have a vm26 going on my pit bike 125cc port and polished. Big cam and "custom exhaust" This info will definitely help with my tuning. Thank you
Thanks for this useful information. I'm trying to tune a mikuni VM carb on a quad bike for a friend. He bought the carb online and slapped it on but it was extremely rich. It had a 200 main jet, I've gone down all the way to 130 and it's still a bit rich. The pilot jet was a 60,ive gone down to a 40 and it's still too rich so I need to get another set of pilot jets to dial it in some more. It seems clear that it's really not the right carb for that motor but it fits the stock boot so I'm working at it to get it right. Hopefully with the information in this video I can get it running well without replacing the entire carb.
What I needed to know was idle lean and Rich adjustment, then mid range lean and rich adjustment, for how far to drop the needle and what difference it makes on the five clip settings, it was helpful to know that they started on the second from top clip stock
Lots of Mikuni's also use an Air Jet located inside of the intake venturi. I believe in the VM manual it is shown as item number 25. Can you explain how the Air Jet works in conjunction with the pilot jet and air mixture screw? Does changing the size of the air jet change the intake vacuum during starting allowing more or less fuel to enter?
This helped me out so much. Thanks. Got a vm36mm putting it on a Suzuki savage 650 off the top of your head I don’t suppose you know a god place to start with jetting
Hello from Florida. If I may ask, I can't find the model number to my carb and the one you're demonstrating with in this video is the exact mikuni one I have that i'd like to clean up and tune. I stopped video at various points and compared to the one i have and its exact screw for screw placement, valves, hose placements, design etc. All of it. Of course like you mentioned jets may be different when vehicle tuning at manufacturer but it's a great starting point for me. Can you help me out? Thanks a bunch. Great video, very helpful. I'm new to carb cleaning, tuning, etc but not afraid to go at it. So if you have the time, you can make my day! I can find manual after model number and do my home work. Thanks again.
I kept wondering why it seemed backwards,..but it's because it's an air mixture screw and not a fuel screw !! I come from minibike race engines and the screw is mostly on the fuel side...thanks for the info !!
Hello, what about the float level? that is a very important tuning factor and nobody show the exact procedure. In my experience, a small amount of tab movement changes a lot in how the bike (and plugs) perform. Thanks
My YAMAHA AG100 1973 uses a mikuni vm20, the float level from carbi side bowl gasket surface, no gasket in place, to the high side of float, when in the upside down position, not pushing needle spring in, is to be set at 19.2mm.
I have a honda xl500. I slow down the idle and turn the pilot screw in till it bogs. Then start backing out looking for the stumble. It wont stumble. So i do i need a larger or smaller jet?
i bought a dirt bike that didn't run at all, after replacing the carb with a vm22, she starts but only with throttle and she doesn't idle at all but revs pretty decent, if anyone knows the issue any help would be greatly appreciated.
Flat slide Japanese MIKUNI carburetor : 24 MM on a built predator 212 motor . Fired right up . Only had to turn idle down . Pretty good for not adjusting anything it's the jets . Hauls ass . Spins the rear tire . 😂👍🏻😃.. I will read the plug and change jets ass required . But it fired right up . So much less aggravation than the Chikaneese copies .
Did the VM 30 s for my Honda CM 400T rebuild. It starts ........awesome .....but with the choke levers down and and maybe for 3 or 4 min. it runs and quits. Now i gotta turn screws or something ?
If there is black smoke come out from your exhaust, then adjust your idle screw. If you have to start your engine with yous choke on, check your pilot jet.
im in wisconsin at 1,100 feet above sea level i have all these jets but i have a dead spot in the 30-40% range on a vm26 i have a 180 main and 20 idle jet i was doing 55 stock and now cant hit 53 so i know tunings off. what do u recommend? ssr razkull 125cc 2018. with exhaust upgrade and uni pod filter oiled up
Hello. Nobody can officially anwser me or understand i have a question about when a mikuni is wide open. The cut air intake side is flush.....but un cut intake side has a bit of a lower hang.......so for max performance should i set them so the uncut side is just above the barrel? Or is it a bit lower for a reason? Thank you and hope you read this👍
What if my idle screw isn’t doing anything? The machine starts and runs. Goes great just doesn’t want to stay idling. Adjusting the idle screw doesn’t raise or lower RMP. Does nothing. Is the slide no set correctly?
Hi I have vm 34's on my CX500 I'm about 10 full turns out with the idle screw ( one with spring around it ) she still seems seems to idle fast. She has straight through pipes. What do I do
Make sure your choke is in the off position, your air screw should be set at 1-1/4 to 1-1/2 turn counterclockwise from seated. Start your engine adjust your idle screw, the one with spring. If that doesnt help, then check your intake spacer for any crack and intake manifold oring, replace them if you can they are cheap.
I have a 1972 Suzuki GT750 with the mikini VM carbs 32 round slide...The problem I have is the slide spring is turning like a wrist watch spring...which goes against the slide... and causes it to turn...when I tighten the top cap down... causing the slide to come out of the grove when I go wide open with the throttle...and the slide doesnt go back down again so the engine goes wide open... ....Is the throttle valve spring seat suppose to keep the spring from turning, which is causing the slide to turn ? I only have this problem with the far right carb... the left and ctr. carbs don't have this issue.............Help!!
So.. I'm new to these carbs becuase I'm new to karting lol but I'm no stranger to carburetors like Holly, Edelbrock, Nikki ECt When I would adjust and tune my idle and mixture I would use a vaccum guage to see the highest vaccum in the engine when I adjusted the fuel mixture screw. On this 212 I'm thinking of drilling a hole to tap in a port right behind the carb to see of I can get a reading. Anyone else ever try this ?
I have a Mikuni VM16 Carburetor on two 110 CC Honda engines. I've had reoccurring issues where I have to tune the carb till the point nothing works and anything past 1/8th throttle bogs and kills the engine. The spark plug always ends up caked in carbon and is wet. I thought maybe my first Mikuni carb was bad so I bought a new one and put it on. Bike worked perfectly for 2 rides, then had the exact same symptoms. I can't get the bike to run passed 1/8th throttle without it dying. At this point, I don't think it is a tuning issue. It is nailed down when I first install the carb but then over 2 rides, it always comes back to the same issue. Could someone help me figure out what is going on here? This is happening on two bikes exactly the same symptoms. So maybe I'm setting something odd? But then what could it be? I've checked for air leaks, throttle cable, the notch on the pin inside (top most seams to work best but still not good), cleaned the spark plug, and checked the float. Everything seems perfect, but still this issue happens.
This still isn’t helping me. I ordered a mikuni carb for my 125 cc Yamaha ttr dirtbike. And it cuts out at about 6,000 rpm. My dirtbike from the factory revs 8,000 rpms. I have a round slide mikuni VM28-49 and I got it on 12/04/18 and since then I’ve tried changing the mixture, I’ve tried idle control, and I’m still to this day trying to tune it and it won’t rev high enough. And also with less rpms come less speed. I have a speedometer app on my phone, and with my old carb it went 56mph with some small upgrades like a lightweight timing chain and performance FMF exhaust system and I left all the on when swapping carbs and not the top speed is 39mph and that’s holding it wide open and it cuts out kinda as if it has a rev limiter but it doesn’t have one. It just cuts out at high rpms and won’t let the engine rev to its full rpms
Your main jet is probably way too rich or the float level is incorrect. Pull the plug out and look at it, it's probably soaked with fuel. Also a VM-28 is way too big for a ttr125. It'd probably even be too big if you were on a ttr-230. The larger the carb is on a 4 stroke the more important it is to have an Accelerator pump. Small cc four strokes get away without one when they're corked up with the factory airbox/lid/exhaust and undersized carb. The vacuum doesn't drop so fast that it can't pull fuel from the jets. Tha'ts what happens when you put a carb that's too big on a 4 stroke. A 24mm would be about perfect, and a 26mm would be pushing the limits. Even if you do get it jetted to run good at WOT, there will always be a slight bog if you snap the throttle open with that big of a carb with no Accelerator Pump. If you figured it out LMK man I wish the best.
The main jet is for wide open throttle high rpm. If it doesn't rev high and has bad wot power (that's main jet). If it dies off idle (it's an idle circuit problem).
My bike will only rev up with the chokes on, it won’t rev with them off. It just goes blahhhhhhhttt and dies. The plugs have always been very sooty and black, which tells me it’s too rich. Since the Mikuni starter circuit is different from a standard choke, is it giving me more air to the mixture while it’s on and throttle opened? Which is why it can then rev with the choke on? With the throttle closed, it will barely idle with the starter circuit on. Been chasing down the tuning with these carbs for weeks. Air screw is almost falling out to achieve a rise in rpms; I have smaller pilot jets on the way. Any help would be greatly appreciated. Honda 400cc with Mikuni VM 32’s.
Agreed, but run the engine leaner, you will replace your engine later, run it richer, it cost money on gas. Try to tune your engine for fuel economy is not an easy task.
I'm having a problem with my bike runs good at idle Throttle is good when started idles fine then dies after get going bogey when throttle is pushed could this be a coil
I have a vm32 and im getting very high idle on a brand new carb i cant lower idle or piolt screw what do i do to lower idle ? Should i turn idle all the way in and turn piolt all the way in im at a loss ?
Choke in the off position, set your air screw 1-1/2 turn out from close, then adjust your idle screw out to lower rpm, dont mess around with air scew until you be able to lower rpm with idle screw. if that not solve yor problem. Then check your intake manifold for crack and intake spacer.
Just did contacted support at www.mikunioz.com/contact-us/?v=7516fd43adaa and got a quick response answering my question, So a big THANK YOU to Mikuna support.
Help me Mikuni'ssss Ive a tmx 38 , brend new but liks on gasket jet niddle, and o ring liks in fuel tube,and the bowl is not drilled.... Wtf is that piece of carb , unregular to jet, niddle cone is f^÷^÷#÷ ... On a brend new 125 tc 2022, a 125 xx fantic 2021, a 125 yz 2021 wtf are the ingeneer ??? Impossible jetting shit Sorry im french im not good in english