yz426 problem

i wonder if anyone can help . my mate as a yz426 and it runs crap wont rev out slutters header getting really hot . right back to the silencer.. i took it apart because i thought he might of blown the head gasket anyway after looking at it i came to the conclusion that it was fine. anyway i did notice that it did have the 450 exhaust cam in it . anyway i put new rings in it new gaskets timmed it back up to what it should be with the 450 cam in it . checked carb cleaned it all out and put it back together and still runs the same . so at the moment im at a loss the only thing i havent checked is the ecu. as anyone had anyone had the same problems

Sounds like its running way lean

Pul the choke out and see if it runs any better. If it does, take the carb apart and slap some bigger jets in there.

if that was the case what as made it go like that . when he first got the bike it was fine . its strange its got me baffled

Lean condition, engine vacuum can suck the o-ring in the intake bell of the carburetor out of place and cause an air leak. Other pieces of the intake tract casn be pinched or loosened and let in more air and cause this. Just my experience with my 426.

Bill

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