28mm Pinasco downdraft carb jetting
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Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 & 96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3839
Location: Oceanside, CA
Mon Jan 04, 2021 11:49 am quote
I got to see a unicorn 28mm Pinasco downdraft carb today. Malossi cylinder from the outside so I知 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知 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稚 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値l 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壇 throw that in and work backwards if theres no info.

Thanks all.
Hooked
1984 PX200E, 1962 Fuji Rabbit S601, 1963 GL, Gilera GSA, Vespa GS160, aTri-ped Micocar, and bunch of mopeds and shifty fifties
Joined: 04 Apr 2015
Posts: 211
Location: St. Louis
Mon Jan 04, 2021 12:23 pm quote
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.

jet chart.jpeg

Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 & 96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3839
Location: Oceanside, CA
Mon Jan 04, 2021 12:32 pm quote
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.
Molto Verboso
Vespa
Joined: 19 Jun 2007
Posts: 1247
Location: California
Mon Jan 04, 2021 12:58 pm quote
Curious about the float bowl to main jet passage wonder if it's less than 2mm like a standard 24e?
Ossessionato
73 & 74 Rally, 76 ET3, 80 P200, 06 PX150, 61 Ser 2, 65 Silver Special, 86 & 96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3839
Location: Oceanside, CA
Mon Jan 04, 2021 1:01 pm quote
No idea. I知 shopping tomorrow the larger jets and I値l 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.
Molto Verboso
2007 Stella 225
Joined: 02 Nov 2019
Posts: 1401
Location: Rochester, Minnesota
Mon Jan 04, 2021 1:14 pm quote
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
Hooked
1984 PX200E, 1962 Fuji Rabbit S601, 1963 GL, Gilera GSA, Vespa GS160, aTri-ped Micocar, and bunch of mopeds and shifty fifties
Joined: 04 Apr 2015
Posts: 211
Location: St. Louis
Mon Jan 04, 2021 1:27 pm quote
MJRally wrote:
No idea. I知 shopping tomorrow the larger jets and I値l 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.
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...)
Addicted
PX 150
Joined: 15 Sep 2006
Posts: 527
Location: Gold Coast, Australia
Tue Jan 05, 2021 5:26 pm quote
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
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