How do I - Mikuni VM22 tuning during break in

[scoot newb]

I am not sure the best way to tune this thing. It is a knock off made in Japan or so the label says.

I guess I should adjust it a bit rich. I really suck at tuning carburetors even CVK ones with one screw for fuel mix let alone this one with both a fuel and air screw. Any advice would be appreciated.

[Alpha Reign]

Originally Posted by scoot newb

I am not sure the best way to tune this thing. It is a knock off made in Japan or so the label says.

I guess I should adjust it a bit rich. I really suck at tuning carburetors even CVK ones with one screw for fuel mix let alone this one with both a fuel and air screw. Any advice would be appreciated.

Read the last page of this article. It tells you what each jet does, along with some advice and tips on what to do. Good luck!

[scoot newb]

Thanks.

[RKG83]

So my buddy and I went to install the same carb and he’s telling me I’m gonna lose my choke option and other things. Did you notice any compatibility issues or is he trippin? I’ve ready plenty of reviews and not a single issue he brought up anyone else has mentioned.

[scoot newb]

Originally Posted by RKG83

So my buddy and I went to install the same carb and he’s telling me I’m gonna lose my choke option and other things. Did you notice any compatibility issues or is he trippin? I’ve ready plenty of reviews and not a single issue he brought up anyone else has mentioned.

You lose the ability to choke it from the handlebars. But it has a choke. Since adding the carb and manifold I haven't ridden it yet. Some bolts still need tightening and I have to install the Grom swing arm bolts, chain tensioners and axle bolts. The carb that came with mine was damaged. Gas just poured out of the overflow and of course, it would not even start. After adding that kit and 110 main, it started right up.

From my reply in the other thread.

Originally Posted by scoot newb

The stock manifold has a smaller diameter. The hole in the head where the manifold connects - It is like they want you to put on a real 26mm manifold.

The stock manifold has a beefy riser part at the bottom where it connects to the head. The new manifold doesn't have that beef so shorter bolts or spacers are needed.

The stock carb has rectangular nuts that are pressed into it. I pried the nuts off and used them to attach the new carb to the manifold. Getting some longer bolts and locking nuts may be a good idea. (see photo)
https://imgur.com/X7Mfy2U

Oh and there is also a bit of throttle play even after extending the adjuster by the throttle.

[scoot newb]

Okay, so i went riding today after adjusting the idle. So far the engine seems okay. The carb needs some more adjustments though.

The problem It bogs when trying to go 1/2 to WOT.

According to this it has to do with the needle and slide. I have no idea how to adjust the slide and I don't remember seeing any notches on the needle to adjust the needle height.

I am at sea level and it is 35F out. Do you think going down a size from the 110 main would help?

[wlfpck]

You need to do a plug chop.

http://www.mikuni.com/pdf/vmmanual.pdf

This is the manual for mikuni VM series.

Search google and youtube for instructions on doing a plug chop. Only way to tell if you're lean or rich and which jets are responsible.

Only other way would be to put in an O2 bung and get a wideband to see if you're rich or lean.

Increase jet size if lean. Decrease if rich. Altitude will play a role in what jet size to use.

[scoot newb]

I couldn't do a plug chop. With the 110, 115, and 120 main jets I tried, there was not way to go WOT. After half throttle it got flaky. For the heck of it, I went down to 105 and it is almost perfect, just after 7/8 throttle it cuts out/bogs. I am going to try 100 and see what happens. I think the air filter I'm running is super restrictive.

100 is working fine. I can use all of the throttle.