Mikuni VM20 tuning/jetting

OK guys let's talk vm20 jetting (why haven't anyone added these to the spread sheet!?)

I know I'm not the only one running these, I have several of them on v1's/garelli/tomos's. I'm also running two vm18's, and unlike the 18's where I have my main jet dialed in I always feel like my 20's are just a hair off.

On my v1's I'm running 170-140 (polini/Meara/73cc Olympia)

175 on my tomos (77's 64cc race kit)

160 on my garelli (polini)

They are all dialed in on the idle/needle, but all feel just a bit off on the main, maybe I'm crazy and just looking to be re-affirmed here but....

What's your jetting?

Re: Mikuni VM20 tuning/jetting

I have noticed that a 4-stroke(ing) mikuni is far more subtle than say a phbg's 4-stroke, maybe that is holding me back from down jetting?

Re: Mikuni VM20 tuning/jetting

Dirty30 Dillon /

Toledo Riot Wrote:

-------------------------------------------------------

> I have noticed that a 4-stroke(ing) mikuni is far

> more subtle than say a phbg's 4-stroke, maybe that

> is holding me back from down jetting?

I've noticed this too. My ZA50 has a vm20 on it and it'll run at good temps with a 165-190 jet. But the 170 I've found gives me just enough of a tiny 4stroke at WOT that I stay there.

A good filter goes a long way, I've found, with getting these dialed in.

Re: Mikuni VM20 tuning/jetting

I agree on the GOOD FILTER

i struggled getting it dialed in with a chitty filter

put on a K&N and whalla

2 @ V1's - both in the 170 ish range

both are slightly rich at WOT

I can feather back the throtle and get a bit more from them,

then if they get hot, i pour on the gas and cool it down.

Re: Mikuni VM20 tuning/jetting

150-165 e50, cali, treat reed, malossi.

I find the differences between jets on mikunis to be very subtle.

Re: Mikuni VM20 tuning/jetting

it used to bug me but then i just got comfortable with it and stopped worring all the time about my damn jets, checking the barometer and hygrometer before leaving the house, having goofy airboxes that could get opened up or closed depending on the season...

Re: Mikuni VM20 tuning/jetting

I run all of my vm's open, never been a fan of air filters, as long as their not forward facing that is.

Re: Mikuni VM20 tuning/jetting

v1

polini - no porting/casematching

vm20 - polini air box filter/weak-ends intake

hammer - blue springs

treats estoril pipe

pietcard yellow coil/2041 box

minarelli p4 head

125 jet & slightly rich

i have another setup, basically the same, but a blue coil and a VM18 (mlm intake) that runs a 70 jet. (edited)

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