mikuni 20mm VM too big for a Polini?!

Looking for some advise here. My last Polini kit I ran a Bing15 which seems to be a very popular combo for Polini 64cc's, but i really want to step it up and really feed this 64cc and also learn a new carb that is more tuneable. I love the fact the Jets can be changed without taking the bowl off. Im pretty set on the VM20. i dont want the VM18 because of the clamp style it is that EVERYONE says breaks off. . The VM20 is the smallest bolt on style carb of the VM series. Which brings me to my main question, is this carb too big for the polini? If its gonna drown this thing in air i dont want to go this route, but if its not too big i'd love to give it a shot. Input fellas?

Re: mikuni 20mm VM too big for a Polini?!

people use tm24's on them. the vm20 is not too big.

Re: mikuni 20mm VM too big for a Polini?!

Also I am case matched for the Polini. Just no porting done to it.

Re: mikuni 20mm VM too big for a Polini?!

Not every vm18 breaks. The ratio of people running them to people who have broke them is probably pretty good. You won't drown it in air unless your jetted too lean.

Re: mikuni 20mm VM too big for a Polini?!

Hepatitis J [OFMC] /

Ryan N. Wrote:

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> the vm20 is not too big.

Also, the vm16 is bolt on if you really are looking for a smaller carb.

They're like 35 bucks on ebay.

Re: mikuni 20mm VM too big for a Polini?!

bings are junk, get a dellorto or mikuni. The bing slide sticks in the carb body and leaks at all joints. my dellorto 24mm is far superior to the 15mm bing, the quality is night and day.

Re: mikuni 20mm VM too big for a Polini?!

🇮🇹💦 Of the Loin /

per Gordon Jennings a 50cc cylinder can run optimally up until about a 20-22mm carb

and a 70 is going to be able to handle up to about a 26-28

Re: mikuni 20mm VM too big for a Polini?!

If you dump enough gas into it- any size carb will work. Maybe you have an old Chevy on cinder blocks you could pull the carb out of.

The bing is no more or less tuneable than the VM20. It just doesn't have an idle jet.

Re: mikuni 20mm VM too big for a Polini?!

I run a VM20 on a V1 Polini. I think it is the largest size you can fit on the intake manifold surface of the Polini kit and have any gasket left.

Re: mikuni 20mm VM too big for a Polini?!

A VM20 would be fine. I ran a VM22 on my AV10 Doppler 50cc kit until very recently (when it snapped in half) and it ran fine.

Re: mikuni 20mm VM too big for a Polini?!

In fact, I'm replacing it with a OKO 24mm PWK in the next week or so. I'm running crazy high RPM though, so your experience may vary.

Re: mikuni 20mm VM too big for a Polini?!

Okay, thank you guys! My question had been thoroughly answered!! VM20 it is

Re: mikuni 20mm VM too big for a Polini?!

Larger slide than piston is where it's at!

Guess the euro 50 shifter racing guys are getting close, they're running 32's on 40mm bore.

Re: mikuni 20mm VM too big for a Polini?!

A good carb has several jets and the slide snaps back like lightning. The bing is a disaster, 1 jet, slide doesn't fit in carb body, leaks at all joints. Saying the bing has equal tuning power, what a joke bings are garbage, that's why everyone tosses them

Re: mikuni 20mm VM too big for a Polini?!

Your bad at trolling. Bings are good carbs.

Re: mikuni 20mm VM too big for a Polini?!

Nick STL Ruffians /

here's my Polini with a 21 Del. my only problem is, when i turn the throttle, it goes forward real hard

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Re: mikuni 20mm VM too big for a Polini?!

40 year old bing carbs are terrible, i agree.

have you tried a brand new one?

i like SHA, the old ones are a mixed bag- same as bing. any new carb will work great but not many new carbs will break in half (mikuni). the bing has a single main jet, needle adjustment and idle screw which means it has ones less facet than the mikuni VM18 or 20 for tuning, but i would hardly characterize the idle jet as an important factor in tunability, right?

i'm not a big fan of bing carbs (i like sha because i run italian bikes), but they're no better or worse than anything else- just different. i think the worst thing about bing is that they're so expensive. i think most people figure if they're going to dump money into a new carb they want something bigger and shinier.

poor bings :'( (edited)

Re: mikuni 20mm VM too big for a Polini?!

Mikuni vm carbs come as small as 12 mm with a bolt on flange. Suzuki fa50 is a 12mm mikuni.

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