I'm having a little trouble with tuning my new mikuni VM22. It's on a predator 212 hemi with black mamba cam and 26# springs. I have the stock pilot and main jets in it, 30 and 100 respectively. I started with the air screw 2 turns out, started it up and adjusted the idle a little high. Then I turned the air screw in which made it about die so I went out to about 2.5 turns out which was the highest idle. The problem is that when I twist the throttle it dies. Any idea on the next step and did I do the idle screw right?
Need help tuning mikuni
- Thread starter maknwar
- Start date
IIRC, there's a third step on the idle adj. You've done two, but I almost think you do it again.
It's in here somewhere.
http://www.mikuni.com/pdf/vmmanual.pdf
Some more reading.
Mikuni carburetor operation and tuning
It's in here somewhere.
http://www.mikuni.com/pdf/vmmanual.pdf
Some more reading.
Mikuni carburetor operation and tuning
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https://www.oldminibikes.com/forum/...13-help-jetting-mikuni-vm22-133-methanol.html
Mikuni vm22-133 on gas, main jet #120-#130 pilot jet #15-17
Mikuni vm22-133 on gas, main jet #120-#130 pilot jet #15-17
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Perhaps this will help. Carb tuning tips for the 22 Mikuni:
https://www.affordablegokarts.com/carburetor-tuning.php
https://www.affordablegokarts.com/carburetor-tuning.php
its not a air screw its a idle jet..all engines are different ,,, with the engine hot and plug clean turn the screw in till the motor stumbles then out till the motor goes rich. set the idle jet screw in the middle of these to extremes where the motor idles at its fastest rpm then reset main idle to your preference
Nate I think you have got it backwards. The pilot set the fuel amount for idle and off idle then the idle air screw adjusts the amount of air going in. While some carbs may work the way you stated mikuni's do not.
Mikuni carburetor operation and tuning see figure 2 for reference.
Mikuni carburetor operation and tuning see figure 2 for reference.
There is too much talk about that air screw IMO. It just doesn't do that much in my experience.
Where is the air needle set at? It definitely affects off idle and all the way up through mid range.
Maknwar, try and move the air needle setting CLIP to the top groove, and try it. If it seems to improve, you are too rich on your #30 pilot jet. Conversely, you could move the CLIP to the bottom groove, and if it ran better your pilot jet would be too lean.
See the link from Ole and BBQjoe, and look at Figure 4. I'm telling ya, this is the most important part of getting them to run right, and will point to which direction you need to go with the pilot jet.
Where is the air needle set at? It definitely affects off idle and all the way up through mid range.
Maknwar, try and move the air needle setting CLIP to the top groove, and try it. If it seems to improve, you are too rich on your #30 pilot jet. Conversely, you could move the CLIP to the bottom groove, and if it ran better your pilot jet would be too lean.
See the link from Ole and BBQjoe, and look at Figure 4. I'm telling ya, this is the most important part of getting them to run right, and will point to which direction you need to go with the pilot jet.
Nagging feeling: Air screw all the way in and it idles fine. Do you have an air leak? If you run the clip all the way down and it runs better, this would indicate a lean condition. An air leak will result in a lean condition as well. I can not tell you if, or how well, the engine should idle with the air screw closed. But this is something to consider while testing things with your air needle clip movement experiment. I wish you the best of luck.
PS: I would never advocate someone use a bit of ether, or propane around a running engine to leak-check to see if RPM increases, because it can lead to fire.
PS: I would never advocate someone use a bit of ether, or propane around a running engine to leak-check to see if RPM increases, because it can lead to fire.
generally 1 1/2 turns on the idle screw, set idle, move screw 1/4 turn in or out till best run. From idle to almost wide open is the slide and slide needle that takes over. The needle should have several grooves in it with a c-clip holding it. Sounds like yours is very lean, try raising the needle one groove. Raise needle or lower clip, same thing. I have seen where a different slide is needed. the shape of the slide matters to a degree. Main jet is for wide open, tho it does influence about 3/4 to wide open. If your slide needle does not have several grooves in it, I have seen some that don't then a richer needle is in order, or if you can try shimming the needle up about 25 thou. Been many years since I was playing with these, and I fried a few brain cells since, so proceed with caution,,, lol
