help on my cr125 2000

Jun 18, 2007
well i just purchased a cylinder on **** as mine is long gone and the cylinder came with a piston ring and gaskets and modifyed valves and all of that stuff yeah. but now i just found out that the cylinder was bored to 57.96mm that makes it a 144cc and when i first got it running there was great compression and i ran the bike in 3-4 tanks 2-3 throttle but then i found out that there was air leakege, now i can not fix this leakage it is from the cylinder to the top end (spark plug connects to) so i try tighting the bolt but it would just not tighten so what i did was replace the gasket still didnt work can somebody help me out please i need help