Vespa px running issues

[AndyS]

A friend is having a problem with his px 200. Standard barrel and carb, JL right hand exhaust, 120 main jet.
The scooter will not tick over by using the tick over screw, it makes no difference if the choke is in or out, I can get it to tick over by winding out the throttle cable adjuster.
It also does not rev out, 4 strokes throughout the rev range, and this does not clear.
I've tried a different carb, but is still the same. I have thought about the main drive seal prob, there is no petrol in the oil, and revs don't rise with drain plug out, but the exhaust smoke is white but not belching it out
Anyone have any other ideas to find out what is wrong
Thanks

[magg]

Sounds like clutch seal. Plug the clutch breather and see if that solves your problems. Mind you, if you have tried to rejet the carb without success before this, it might still not run properly.

If it does the seal is blown, and you need to replace it.

If it doesn't, look elsewhere..

but I'm pretty sure that is the clutch seal letting oil and air in to the crank case.

[AndyS]

Thanks ill try that and see how it goes
It was apparently running ok before with the jetting and pipe

[AndyS]

I plugged the clutch breather and it just seems to be the same, 4 stroking and unable to set the tick over. Is there anything else I could check, don't want to strip the whole engine down for no reason
Thanks

[cit205]

If it was running ok before the jetting and pipe then i'd change it back to eliminate those.

But it does sound like main seal failing.

[AndyS]

An update, following re seating the carb and the head its fine now, it looked like it was probably leaking.
from the cylinder head