400EX misses at top end. PLEASE HELP..

[dirtyrooster]

My uncle's 2000 400ex misses real bad at top end. valves have been adjusted and we swapped his cdi box out with mine along with completely disassembling the carb and cleaning it. All of this didnt change anything. Could the cam chain tensioner be the culprit? PLEASE HELP!

[JOHNDOE83]

It could be the plug wire or the coil, did you stick anything in the main jet to clean it. Its possible to make it bigger and possibly make it to rich if you do that.

[dirtyrooster]

Its got a brand new plug too. I havent checked the coil cuz im new to the 4 stroke scene and when it comes to electrical components im clueless. where is it located?

[buddy willard]

follow the plug wire?

[jkosakowski]

Im gonna say coil because mine started to do that so i changed the coil and the problem was fixed.

[suspension101]

I've only seen this happen a couple of times but I've had bad flywheels that will cause this. I have also seen pieces of metal on the flywheel or pick up coil that will interrupt the signal at high rpm too.

[dirtyrooster]

Thanks guys! We're gonna look ino it