Mikuni VM20 jetting.

Barry (Bob) Brown /

Hobbit

DR 70cc kit w/head

VM20 w/MLM intake

Any Idea what jetting to start with? It runs great with whatever was stock, but I'm not sure if I need to move up from stock jet. I got a range of 110-155 but reading on here others I see are runnin in the 180-190 range?

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Re: Mikuni VM20 jetting.

I'd start with the 155

Re: Mikuni VM20 jetting.

If it runs great , why would you even think about other jetting ?

Re: Mikuni VM20 jetting.

Barry (Bob) Brown /

I've only run it maybe a mile and don't know if it may be lean or? and it was running upwards of 410º so was thinking upjetting may help?

Re: Mikuni VM20 jetting.

Think about timing , as that can also cause heat .

Re: Mikuni VM20 jetting.

Michael Forrest /

yeah if its running hot then increase the main jet and then ride it a while and then check the spark plug color

Re: Mikuni VM20 jetting.

stock on vm20 from treats is 180.

Re: Mikuni VM20 jetting.

Barry (Bob) Brown /

So wasted 27 bucks on jets...lol

Re: Mikuni VM20 jetting.

> Barry (Bob) Brown Wrote:

> -------------------------------------------------------

> So wasted 27 bucks on jets...lol

Maybe you'll use them on the next bike .

I still have jets a 'acquired' back in 1972 .

It's not like they have a short shelf life . ;) (edited)

Re: Mikuni VM20 jetting.

If you take one of your smaller Jets and drill it bigger than the 180 it will never hurt anything.... But it's all about that needle I keep it in the center and make sure you tune that airscrew.... I found the easiest way to tune the air screw on the mikuni VM carburetors.... Is by starting your bike up and letting it get to correct temperature.... Then adjust your idle screw so it's idling high and fast..... Then take that are screw and by starting it around a half a turn out keep on turning it until your bike idles really high and fast... You should be able to keep turning until it starts to come back down... If not your jets are too big.... But either way three or four or five turns out and then adjusting your idle back down using the idle screw....Will definitely help in getting a faster response... I ran the mikuni vm18 for almost a year and it ran great but as soon as I find tune that screw oh my goodness it helped with everything... Plus I install the four petal reading take that did wonders ripping dicks now...

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Re: Mikuni VM20 jetting.

Barry (Bob) Brown /

> Joseph Waldridge the 2nd Wrote:

> -------------------------------------------------------

> If you take one of your smaller Jets and drill it bigger than the 180 it

> will never hurt anything.... But it's all about that needle I keep it in

> the center and make sure you tune that airscrew.... I found the easiest

> way to tune the air screw on the mikuni VM carburetors.... Is by

> starting your bike up and letting it get to correct temperature.... Then

> adjust your idle screw so it's idling high and fast..... Then take that

> are screw and by starting it around a half a turn out keep on turning it

> until your bike idles really high and fast... You should be able to keep

> turning until it starts to come back down... If not your jets are too

> big.... But either way three or four or five turns out and then

> adjusting your idle back down using the idle screw....Will definitely

> help in getting a faster response... I ran the mikuni vm18 for almost a

> year and it ran great but as soon as I find tune that screw oh my

> goodness it helped with everything... Plus I install the four petal

> reading take that did wonders ripping dicks now...

Thanks, I havent started tuning the carb yet, but I do think a 180 might be too big to start.

Re: Mikuni VM20 jetting.

Michael Forrest /

tell me your max RPM and engine size and I'll tell you the idle and main jet. Do you know which needle you have?

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