speedfight loss of power

ok so im new to the forum and i think its a grea forum so far and have decidedto put my problem to you guys.
My ped is reasonably quik and has power untill around 33 mph but after that the sound changes and the speed still goes up but no real power what could i do to get that power up

 

could try different rollers clutch spring

 

try cleaning out ure carb.. whats the spec of the bike??

could also try a roller change probs got flat spots on them

ben.

 

^^^agreed,, most likely rollers worn or belt,, tired clutch springs