Engine Trouble engine runs bad please help

[tacotyler]

okay guys i have a 80cc china that ran great for a year no problems 1543 miles on it no problem i have a upgraded carb (rt) and a cdi of a old suzuki quad witch worked great higher, faster rev, ran cooler and more power. now one day i took it out and it started bad and while leaving my neighborhood, there was no power i would ride at a constant speed pull in my clutch lever THEN THE ENGINE WOULD REV REALLY HIGH THEN DIE for no reason? i checked for intake leaks none, cleaned my carb, checked plug witch was lean, checked for any head/cilinder leaking, i have the same compression. i put the old cdi on witch the engine still ran bad same problem. i just don't no what could make my engine with no load rev really high then die, i thought it might be a intake leak. okay well i think there could be a small seizure on the exhaust side causing drag witch could be making it run bad? i dont what it could be so any help would be awesome thanks

 

[Purple Haze]

You definitely have an air leak somewhere. Maybe one of the crank seals. With that many miles on the engine, I'd go ahead and change the bearings while you're there.

 

[crassius]

yeah, sounds like a loss of compression - seals, or head gasket, or case gasket, or rings

 

[Deleted member 12676]

with mini-seizures often the rings stick in their grooves. take it apart and clean it and clean out the ring grooves.
I would bet on you having a crank seal leak though

 

[HeadSmess]

ditto on those crank seals. check magneto/clutch housing for oil/fuel.

if concerned about cylinder state, pop off head and check bore at BDC. any damage will be apparent and warrant further inspection... there will always be a minor scratch or two. ignore them