knocking sound on yz250??

[CowsBitePeople]

Ok i have a 1993 yz250 that starts up easy when it is cold but has trouble starting when it has been ridden for morw than a few minutes....i jumpstart it usually if im on a hill otherwise i wait for a while....well i started it up today and got off to look at the engine while it is running and i can hear a knocking sound....not sure how to explain the sound kind of like the freewheel on a bycycle just speeds up when i revv it ....i cant hear it when i sit on the bike only when my head is at engine hieght....The bike runs strong and stuff but i just want to knoe why it is makeing the sound and why it wont start well when warmed up.... :confused: Anmy help would be great Thanks

MaTT....

[CowsBitePeople]

Any one??

[hondafox440]

Detonation, or knocking is most often caused by too little octane in the gas. Are you running 93 pump gas? Your jetting may be slightly lean. If that doesn't help, it may be piston slap and time for a new top end. Your powervalve assembly may be all gummed up as well.