Had my cambelt changed a month or so ago, and had hardly any power. Got it checked by my dad and it was ever, ever so slightly out!He adjusted the dizzy and had the same problem as yours. I'm not too good on the technical words, but when the top pully is tightened, the bottom one would ever so slightly adjust ( if you understand) and puttin it out of time..or that just happened on mine.need a pair of hands gripping that bottom pulley if so. or maybe your marking is slightly out? hope that helps, in some undetailed way.lol