Mikuni jetting on 250

[atreyu]

I was going to email Nigel (Lacey) but I don't want to pester at the moment after seeing the notice on his site.... so perhaps others can advice in the mean time?

I'm after the base jetting for a Mikuni VM32 on a 250 racer
It's using an Omega piston, 40x36 valves, Piper 173 cam and "basic" flowing of the head.

[pptom]

I can't directly help, but I'm also very interested on any feedback for this.
My engine is a similar spec to yours, maybe slightly de-tuned (omega 'road' spec piston, big valves, head work and a green and white cam). Fired it up for the first time since rebuild last weekend with the brand spanking new Mikuni which was supplied with standard jets.
Tickover wasn't too bad but not perfect and it seemed to rev OK under load - it was certainly good enough to check the timing at full advance.
I'll not be running the bike until the early part of next year + don't mind mucking about with jets etc, but it would be nice to know if anyone has ballpark jet sized to start with.

Oh, and while I think about it - what solution do you have for an air filter / velocity stack - my carb inlet sits pretty close to the frame, not sure what I can get on the end of it.
Tom

[double diamond]

Might try contacting Eric Pritcherd (eric@rocler.com). He was running both 250 and 350 Ducatis and I believe used round slide Mikunis. Matt

[richied46z]

I might be able to help. I'm vintage motocrossing a 250 n/c with AHRMA in Northern California. I have been a fan of 32mm Mikuni's on 250/350 engines. I've talked many of my customers into using this set up. They work great for street or track. My engine uses a MegaCycle cam with a twin plug big valve (36x40) head, high comp piston, and total loss ignition. This bike pulls hard from the bottom to the top.
Here's what works for me at about sea level.
Needle 6DP17
Needle Jet 159 Q-5
Pilot 30
Mian Jet 190
Slide #3
I also set my timing at 32 BTDC
If you're a roadracing you might go bigger on the main jet.
Good luck!
Rich Dominguez AHRMA #46z

[pptom]

Many thanks Rich, that's really useful info.