Carb prob.


I have a Polini 177 with longstroke and Malossi reed and I have just ordered a keihin 28. I put it on with the standard jetting, it seams already much more smooth then dell’orto 28, but there is something wrong at iddle can’t find the right set up and it seams a little empty even if smooth at mids and can’t iddle well whatever I do.
My carb set up is:
main 132 (it was 135 standard)
slow 35
needle JJH

I drive it with RZ rh.

I don’t know what to do and the scooter center where I took the scooter to try to solve the problem it seams they just loose time and then they ask me why I have bought this carb, it is not good for vespas.

tank you Curare,

I have these jets but not the needle. Tomorrow I will try it.

How do you know this carb was from CPW?


it is just a standard setting…
I said CPW since I know them. No, not magic.

hello costabravo,

if they told you that the keihin PWK 28 is any good for vespa is because either they want to sell you something else or because they don’t know it. The Keihin is vastly superior to a dell’orto 28.
So you don’t have to worry.

The set up of your keihin is not a good set up for your engine. It is ,more or less the standard set up they sell it at same specialized american center as CPW.

Change the main jet with a 128.

And don’t worry about sizing it will be good, I promise.

The slow jet is too small get a 42 or a 45

With a 42 you will exprience with your engine (polini 177 with reed and longstroke) a small hole if you open full trottle from iddle. You could use a 45 but then
in the transition from low to low mid you will be not as smooth. This you could solve if you change the cut away valve from 3.5 to 4, or better if you change your exhaust. The rz rh is a very good exhaust but with normal stroke.

In your set up I would use a SIP evo with a HP4 flywheel.

And I would change the needle from jjh to jjg clip 2nd from top.
With the jjh with your combination it would work but you won’t get it perfect.