Gilera gsm 50 problem

[blair2]

hi there i have a gilera gsm 50 (50cc 2 stroke)

bike was perfect when i bought it, running perfect but the only problem was that it was spitting alot of black oil out the exhaust. So i looked up how to resolve this and found out that doing a top end was my best bet. So i did this fitted the piston perfectly, now the problem

when i close up the top end with the gasket and tighten the bike will start first kick but when i put it into first it moves very slowly and is in no way ridable

so this got me thinking it was a compression issue but if that was the case it would have a hard time starting and not start first kick

side note: replacing the piston did not solve the oil issue.

help would be appreciated thanks

[Tamsin]

Is the bore of the cylinder nice and smooth?

[blair2]

yes in good condition