To start with it would be worth checking out the following O rings:
- under the starter, inlet manifold to crankcase, carb to inlet manifold
After that I would remove the carb and carefully inspect the body of it for cracks or damage, under the back cover is a rubber diaphragm and sometimes they can pul in allowing it to suck more air.
The plastic carbs are pretty good in my opinion, there are plenty of worse ones to work on out there.
Cheers. Joe.
