Modern Vespa

Hi,

As i am soon going to have the engine out to swap my exhaust i though id ask for advice on this as i'll probably pull the engine to do it.

I had an intake leak when i first got the PK but i thought i fixed it already. There were one and three quarters of an intake gasket so i removed them and put in a new one i cut and this problem seemed to dissapear.

The problem shows itself in two ways:

I just ride along like normal, and when letting go of the gas it will just keep going like some sort of weird cruise controll. This can keep going for quite a while, usiually falls out of this behaviour with an increase in load like applying the breaks or a hill.

The other way is that i will ride around like normal, i come to a stop, plopp it in neutral like normal and it just starts revving to the moon without me touching the gas. Seems more common when on an incline. I have never let it just go off until it sorts itself, always stop it with the clutch and breaks.

I had both of these happen today and it is quite unplessant when in stop and start trafic and the Vespa want to hug the car in front of you unexpectedly.

The thing i dont really understand is why it only happens from time to time. Today it was almost omnipressant on my commute but yesterday it didnt happen at all. Only difference i can think off were that i gassed up this morning and that the outside temp is 2c warmer today.

Engine is stock besides slightly richer jets.

Any clues where to look next? I will inspect the intake gasket again but other than that i am lost. I have checked that the cable and slide are free and return even when pushing on the slide or doing other dumb stuff to make it bind.

Check there is gear oil in it. If no or very low gear oil it's serious.

Sure sounds like an air leak.
Binding slide/cable wouldn't fall out of behavior under load.

Before rebuilding my smallie it would do that, randomly like you describe.
Manifold to carb leak.

Do the PK's still use the aluminum slotted sleeve, felt ring?

thankfully, no.

It is dripping out so there is for sure some in there

Good reminder to top it off whenever i swing by the garage though!

No felt ring, really confused me when i first wrenched as all the info i could find had that and were comparing where it should be and what for ect.. and i just didnt have it.

Could be the intake gasket still, i dont remember if i had a spare or if i cut one myself. Could be that it broke or was cut from a non ideal stock that is too thick or something. Should have added one in my order for the exhaust but i forgot.

If there is a template somewhere i could cut a new one in the lab where i have better tools for that kind of stuff.

The weird part is that it is so intermittent. Had it happen two times on my morning commute today. Yesterday it was many more times than that. Two days ago it was none.

Just to follow up here for anyone who experiences the same:

It was an intake leak. The intake gasket had been cut up around the holes by damaged nuts. Basically the gasket was folded over around the holes making the seal worse.

The intermittent part i guess was from all the goop surrounding the intake manifold keeping the air out most of the time.

I cut off the folded over part as the rest was good, cleaned up the nuts that caused the issue in the first place and put it back together. So far so good!

One of the best gaskets I'd tried is SIP blue. But it seems you can't buy separately only intake gasket. Only clutch cover one.
So you can buy their paper(I did the same). Or this Polini gasket.