Modern Vespa

I got to see a unicorn 28mm Pinasco downdraft carb today. Malossi cylinder from the outside so I’m guessing its the 220cc kit with a rotary intake and a re-welded sito box pipe. A P200 metal air filter had been hogged out and installed. Surprisingly a stock 200 airbox cover is installed as well. Not the taller Stella/ Pinasco air boxes.

It was jetted like a 24mm carb 160, be3, 130. The new owner knows nothing about Vespas so I’m trying to jet it on the conservative side for reliability/ fun so I threw in the richest combo I have 120, BE4, 135. Still revs out cleanly.

I couldn’t find anything out there on the English speaking internet boards as far as jetting info goes for the downdraft 28mm. Obviously I want to jet rich for this guy as Southern California temps will increase and he’ll start pushing this more and more the more familiar he gets with it.

Anyone got any experience with these? Richest main jet I can buy from Scooterwest is a 155. Figured I’d throw that in and work backwards if theres no info.

Thanks all.

I am running a pinasco 24.24er, mallossi, long stroke pinasco crank, BGM exhaust, polini velocity stack, stella airbox with spacer. on one bike. I have a 160/BE3/145.
Similar set up with a modified HRA cylinder, polini box, pinasco velocity stack, and pinasco airbox has the same stack of jets.

I would assume you would need a larger main than my 24.24er, but velocity stacks made for a bigger main jet jump than I thought they would on both of these bikes.

In a thread I just posted I learned about a sizing difference in SIP and dellorto jets, be aware if you were not already.

Roger that. Saw your thread this morning.

Ill definitely shy away from the velocity stack with this guy. The 28mm definitely gives it enough CFMs without the need to accelerate the air in.

Curious about the float bowl to main jet passage wonder if it's less than 2mm like a standard 24e?

No idea. I’m shopping tomorrow the larger jets and I’ll see the guy Thursday.

Hopefully they drilled it larger so the larger main jets can actually get the fuel they need and not be choked down from the bowl.

Pull the main jet completely out and see if it still revs out, at least then you know your not chasing your tail trying to get to a point that doesn't exist.

https://www.scooter-center.com/en/carburator-pinasco-si28/28er-vespa-largeframe-px-sprint-rally-cosa-vna2-vnb-vba-vbb-gt-gtr-ts-super-pn26295020

Worth checking, but they are drilled out larger on the Pinasco 24.24er, I can't imagine they would not have done this for the larger carb. (Except I actually can imagine this, seems like I am constantly surprised by aftermarket performance parts. Eg: There are no oil holes to these bearings, this cylinder needs X/Y/Z...)

My mate runs a quattrini232.
Tried all different jetting options on a Pinasco carb but starved for fuel no matter what we did.
Reed valve and phbh30, problem solved