I have a China girl 80cc and had lots of issues with it 4 stroking. I went ahead and bought a bike berry HP carb and it runs way better but there is still some 4 stroking at WOT. It runs almost perfect around 1/2 - 3/4 throttle then 4 strokes. I have sealed all of the gaskets with some more high temp gasket maker so I know it's not an air leak. Also the bike seems to run a little slower when its warmed up compared if I ride it when its warming up. Running 24:1 and have probably ran 1 tank of gas through it. Maybe it's just 4 stroking during the break in period?