Modern Vespa

I know I've posted a similar thread recently and don't want to appear a pest but I've been rethinking my high revs problem and tried to understand what was happening to scooter. Some people who responded to my post of 'high revs when idling' suggested an air leak which could have been flywheel/clutch seal, cylinder head, carb etc hinting at replacing gaskets or/and correctly torquing engine parts and replacing seals.

I appreciate it isn't an easy problem to diagnose if scooter can't be seen or heard, however I'm not so sure I explained the problem well enough which I apologise for. So here goes again:

Scooter kickstarts 1st/2nd attempt and sits idling fine, then after several minutes the revs increase. When I open throttle thinking I might be able to stabilise revs the scooter stalls and engine cuts out as if it has flooded. Scooter then takes a few kicks before it starts again - making me think it has flooded. If this is a more accurate description of the problem is it possible that something is going wrong in the carb rather than an air leak.

The jets are standard and correct for a PX200E although the scooter does have a simonini exhaust which I was told did not require a change of jets. Is this correct information? Can I drop the jet size if too much fuel is passing through engine?

I have cleaned the jets and the air filter.

I have a new B7ES spark plug although the last plug when I bought scooter was a BR7ES which was wet and oily, which makes me think either plug wasn't igniting properly or mix is too rich. Not sure if this could influence my problem?? Can fuel residue from poor combustion cause flooding? Where does this fuel go, does it just get spat out the exhaust or am I talking bollocks?

I have checked the carb slide and it appears to function as it should snapping back when I release throttle.

I was wondering whether the carb float/needle could be an issue here causing the engine to flood with petrol and choke it.

Or maybe replace the jets with new ones. Can the jets malfunction in a way which could cause carb to flood and cause increase in revs?

Don't know if anyone can shed any light on this one and give any further advice. Thanks, as it's getting darker ,wetter and colder here at night and I don't have a garage to work in so not as much time to spend tinkering with scooter. Sorry people still a bit of a novice in all this mechanic melarkey but I can only learn if I ask, just hope I'm correctly diagnosing problem and asking the right questions so please forgive me!!!

Kind of a shot in the dark because, as you say, I can't hear it.

My thoughts are the idle increases when the engine warms up - this is normal, though it shouldn't be alarmingly fast. I have mine set so that it's a little above stalling when cold, but idles easily when warm.

The stalling when you give it gas leads me to believe that your main jet might be clogged. You open the throttle, that pulls more air/fuel mix through the main, which will starve the engine if the jet is clogged and not enough fuel gets through. Clean your jets if you haven't, see if that works. If not, clean your carb, there might be a clog between your float bowl and main jet, though we know the idle jet is working.

I would not step down a jet size if you have an aftermarket pipe and have not plug chopped. Likely you will end up stepping up a size or two once you do.