Ive read and tried everything i can find special thanks to Mr. Don Grubee 2010 66cc GT5 POS A little backround. This is my second GT5. My first was great except the rear motor mount bolts sheared off leaving the chain to hold motor in place. Lots of vibration. So I decided to buy a new one as gasbike.net had sent me a discount email. 20 days later I was installing on my new Specialized Hard Rock. CNS carburetor NG. Backfire caused head gasket and bottom cylinder gasket to blow. I only realized the head gasket. Head bolts not torqued by factory. I took two off with my fingers. Put Speed carb from old motor on and sealed head, intake and exh. Did not fix lower cyl gasket. Engine very loud. Significantly less power than old motor. Ran for 1 week. Bolt holding crank gear (clutch side) worked its way through cover and fell off inside. Tried repair on side of road but chinese hardware failure (flat/phil pan head cover bolts) stripped. Somehow I made it home. The gear must be pressed on or something b/c i rode all the way home with no bolt in it. Repaired that with old parts, and ran for several more weeks. Having problems with fuel mixture. Engine seems to run out of gas going up big hills. After boggin it up a hill, engine goes full RPM for 10-15secs and then idle goes up and down drastically then dramatically then annoyingly and then calms down and idles. Sometimes stalls. Internets says go leaner when hot/humid. Order several jets .66,.68,.70. While waiting for jets I discover cyl sleeve gasket leak and repair. Engine sounds much better now but mix prob is still bad. Jets do not solve problem. Order .74,.76,.78. THEN, Riding home from corner store i reached 28mph. Fastest Ive been. Running pretty good..... HASN'T RUN SINCE. Tried the following to remedy: new cdi new performance wire new mag coil brushed varnish off mag coil sanded grounds down to bare metal disconnected kill switch checked with voltmeter blue to black plug out 1200rpm drill = 49vac grounds good spark good fuel flows from bowl drain well plug is wet checked magnet against old motor magnet = same blew out carb with compressed air ALL orifices clear installed o ring @carb intake regasketed intake/cyl sleeve checked mag install blue=top white=bottom checked keyway TDC piston TDC installed hi flow tank drain and new fuel filter installed .66,.68,.70..72,.74,.76,.78 jets NONE of this worked? I have a new NT new old stock carburetor coming from china. If that doesn't work, i don't know what i'm a gonna do. I can't even think of anything else to try.