i have been reading this thread because my puch has been having a similar issue.
it was working just great up until a couple weeks ago. on a drive across town it started slowing down its max speed (it usually goes at least 30 on a long straight flat road but this time it could only get up to 25) then shortly after that the engine stopped altogether.
i can start it and idle it just fine (except it idles fast now), but when i turn the throttle to rev the engine, the engine stops. i am quite new at engine troubleshooting. this puch was going to be my learning tool. it has had a slow gas leak since i bought it (about a month and a half ago) and i tried to look for where it was coming from. i may have changed the flow regulator screw in the process, but i have readjusted that screw since then to try to fix the problem with no success at all.
i did notice that the carb is leaking a little bit when just sitting there.
as far as i can tell all the engine parts are stock. so it makes sense to me that i shouldn't have to replace a part unless it's broken. all the stock pieces if working properly should keep the bike running as well as when i first bought it (presumably as well as when it was first made).
to me, my problem sounds very similar to rob's. should i be looking at the carb and the exhaust as possible sources of the issue?
any help is greatly appreciated