this is killing me

[yz80nbeast]

i have a little pit bike 70 and i have had it for a while, but it has lost power, i know this because my friend has the same bike and his has more power than mines, to test it we put my 110lb friend on mines and he can beat the other bike but with me on it(my bike) he comes blows right by, but when he first got his bike me and him would race and who ever got the better start would win the race(drag races)


things done to my bike:
new piston rings, cleaned piston, performance air filter, ngk spark plug.

things in his bike:
new piston and rings.



my bike also seems like it is sucking in too much air cause it sounds really deep compared to his but i thought it would with air filter but it wouldnt hurt the bikes, power

 

[CarnageZ28]

Probably running slightly lean and wearing rings out faster? Do a compression check. If compression is good, you can rule out something mechanical, and assume the possibility of worn reeds, misjetted carb, weak spark, timing.