changed belt now bike wont accelerate

hi, i recently changed the belt on my speedfight2 the old one is noticeably thinner than the new so i guess it was pretty worn out, but when i finished putting the new belt in i went for a drive and now it wont accelerate anything like it did before up to about 30mph passed that its fine. do you think i should put lighter rollers in, what do you guys suggest?

 

Give it a chance to wear in, they all do it when a new belt is fitted. It should take 100 miles or so.

 

the belt is gripping tight as its new and slightly wider.. it will wear down after a good long ride and slowly improve performance