Runner SP 50 Cutting Out

Hi People
im having problems with my runner sp50
when i start the bike it runs fine on tick over but when i take it out for a ride its got no power & want get no top speed, hits 30mph and then just cuts out on me ( dies )
ive changed my main jet from 53 to 60
got it derestriced
got a polini exhaust ( derestricted )
got a polini hi speed variator 6.3gr rollers

if anyone can help me or has had a simular problem please HELP
dnt wanna get bus to work anymore

Thanks

 

whats the compression like mate ? could possibly be the piston rings

 

UP +1
Or maybe rollers got out or stuck?

 

rollers seem fine when i checked & i dnt have a clue wot the compression is like but im going to put a 70 kit in this week plus bike wont start at the moment anyway
thanks for the replies

 

Check the carb, float ok and fuel system.