99 YZ80 bogs out at high speed

[Austin94]

Hello. My son's bike is bogging out at high speeds. It used to hit the speed bands and really take off, now it won't even get to them. We have changed the jets, cleaned the carb, repacked the exhaust and it still won't work. I am new to this whole dirtbike thing and could use any help.

Thanks a bunch----Beth (Austin's mom)

 

[chevy383cid]

You need to get a compression reading, It sounds like it's low , It should be between 135-160,It might be time for a topend rebuild!! Wich won't be to costly,If compression is low ,pull the cylinder off and look at the cylinder walls, if they look in pretty good shape-scotch brite or lightly hone it-and order a new piston,ring,pin,and pin bearing-or just a wiseco piston kit, Don't forget the gaskets.

 

[gergetz]

yep you need a new top end done!

 

[QKENUF4U]

could also be way lean since he said he changed the jet. but compression is def. a possiblitly