80cc polini/mikuni vm20 tuning

Jack Bartow /

Mar 27, 2019 03:03PM

Hey y’all, I got a 80cc polini kit on a minirelli V1, that treats vm20 party pack with a people’s pipe. I’ve been riding it at main jet 150 and idle jet 22.5 and would only cut off on me maybe 15-20 minutes into a ride once I let go of the throttle.

I threw on a 180 main and a 20 idle based off of someone else’s similar build around my area. The thing was just barely harder to start and seems to ride almost the exact same. Just has a slightly higher idle rate. Is this normal? I jumped way up high and barely feel any difference other than slight bog at 1/2 throttle while accelerating but blasts immediately after. What are your set ups and if you have any tips I’ll take em i feel pretty confused about all this. Thanks!

Here’s a video of three idle rates

https://imgur.com/gallery/cQIggFB Do these sound alright?

Re: 80cc polini/mikuni vm20 tuning

Mike Boyd /

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boyd

Mar 27, 2019 03:24PM

Tune to the main jet at wide open throttle. Once that's dialed in, tune the mid range using the needle position. Then tune the idle using the idle jet and fuel mixture screw.

Re: 80cc polini/mikuni vm20 tuning

Graham Motzing /

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grahammotzing

Mar 27, 2019 03:31PM

haha yeah this is one of the 'problems' people have with tuning VM 20's and 22's... the just kinda run meh no matter what jet is in them until you hit the right jet, then they blast.

they are super forgiving to get the bike running but that can be a problem because you can be jetted way off and not know.

you will have to probably do a real-deal legit plug chop, also get your timing dialed in. If you're not super confident in your tuning abilities get a temp gauge and use that to be your guide.

also double check for air leaks, i dunno your whole setup but every time i've put a vm20 or 22 on a moped it has been 145-165 jet.

Re: 80cc polini/mikuni vm20 tuning

Dirty30 Dillon /

hydra

Mar 27, 2019 03:38PM

> Graham Motzing Wrote:

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

> haha yeah this is one of the 'problems' people have with tuning VM 20's

> and 22's... the just kinda run meh no matter what jet is in them until

> you hit the right jet, then they blast.

>

> they are super forgiving to get the bike running but that can be a

> problem because you can be jetted way off and not know.

>

> you will have to probably do a real-deal legit plug chop, also get your

> timing dialed in. If you're not super confident in your tuning

> abilities get a temp gauge and use that to be your guide.

>

> also double check for air leaks, i dunno your whole setup but every time

> i've put a vm20 or 22 on a moped it has been 145-165 jet.

Nail on head. The VM series is a easy to start, hard to fine tune in. I personally blame Mikuni's design which really effectively meters itself through vacuum pull, whereas a PHBG will be three main jet sizes off and no t even start.

Re: 80cc polini/mikuni vm20 tuning

Jack Bartow /

jackbahtow OP

Mar 27, 2019 03:38PM

I have noticed the on my temp gauge that it shoots up to like 200 within maybe like 2-3 minutes of slowest riding. The kits basically brand new and didn’t know if that was just normal for new cylinders to heat up when breaking in

Re: 80cc polini/mikuni vm20 tuning

Graham Motzing /

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grahammotzing

Mar 27, 2019 04:19PM

> Dirty30 Dillon Wrote:

> Nail on head. The VM series is a easy to start, hard to fine tune in. I

> personally blame Mikuni's design which really effectively meters itself

> through vacuum pull, whereas a PHBG will be three main jet sizes off and

> no t even start.

yeah man, you and i will always disagree on this, i would say its a much better design because its more forgiving and runs pretty good no matter what. there is a reason that dellorto is basically out of business and Keihn and Mikuni have dominated the motorcycle carb world for the last 50 years. They also cope way better with environmental changes and that is pretty hard to argue with even if you don't like the fact that they are forgiving on the main and needle jetting.

Re: 80cc polini/mikuni vm20 tuning

Dirty30 Dillon /

hydra

Mar 27, 2019 05:11PM

> Graham Motzing Wrote:

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

> > Dirty30 Dillon Wrote:

>

> > Nail on head. The VM series is a easy to start, hard to fine tune in.

> I

>

> > personally blame Mikuni's design which really effectively meters

> itself

>

> > through vacuum pull, whereas a PHBG will be three main jet sizes off

> and

>

> > no t even start.

>

> yeah man, you and i will always disagree on this, i would say its a much

> better design because its more forgiving and runs pretty good no matter

> what. there is a reason that dellorto is basically out of business and

> Keihn and Mikuni have dominated the motorcycle carb world for the last

> 50 years. They also cope way better with environmental changes and that

> is pretty hard to argue with even if you don't like the fact that they

> are forgiving on the main and needle jetting.

We're both saying the same thing my dude, I actually like mikunis alot for all these reasons. It just takes that extra bit of time to dial in because the self-metering is really

Re: 80cc polini/mikuni vm20 tuning

Graham Motzing /

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grahammotzing

Mar 28, 2019 12:20PM

roger roger!

i took your advice and grabbed a CP19 to throw on my polini for this summer, interested to try it out. I thought they were a PE clone but they are pretty significantly different. Haven't even opened up to see if it takes the same main & pilot jets...

MOPED ARMY

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