Hi

I've recently fitted a Mikuni VM26 to my 1979 Sherpa 250 , unfortunately it appears to be run a tad rich. 

Its running a 35 pilot jet and a 130 main, I've worked the circlip on the needle all the way to the top notch  and althought its now running a lot better its still rich and requires very little choke. 

What jet sizes are being used by anyone else with a Vm26 on a 250? 

Hi there, maybe worth checking if you have the 'correct' jet needle and body. 

......from your symptoms, I wonder if your throttle slide has too small a cutaway, again various sizes available. 

Good luck. 

This is what I used for 199A

Idle   

Idle      30

Main   140

Needle 5C23

Needle jet O3

Throttle valve 2

Basically as it came from France Classic Trial

Yes, it runs rich at small throttle setting but needs choke when starting from cold

If changing to 2,5 throttle valve I guess the needle and needle jet has to be changed but have not tested. Now runs OKO

Edited December 4, 20214 yr by carl ekblom

I don't know why, but I could never ajust a Mikuni VM for a trial bike. I had no problem for MX or dirt track bike. Mabe Carl Eklom solution ( OKO ) is the best.

Guy 

I think the Mikuni VM was quite good for my 199A. However, might need some fine tuning, and adjustments to float level, as I always had problem with sudden engine stops when going slightly downhill. The sound indicates too rich mixture at low throttle setting, but runs well. And the Air Screw is on the right side😕

OKO (mid-atlantics) sounds good and runs good. I found the airfilter (inside air box) and connection to carb to be important. I use OSSA tr80 airfilter and a small platic tube inside the air box rubber as a connector to get it all working.

The OKO has idle and air screw to the left

Let´s see later next year if I still prefer the OKO

If you test, pay attention the OKO is flat slide. Make sure it is permitted if you want to compete.