High RPM vibration/rattle in 400EX?

[rr4406pak]

Hey EXRiders!
I have a strange problem with my 2001 400EX that has recently surfaced:
When I am at high RPMs winding out the gears I get a high frequency vibration/rattle, but only at high RPMs. It feels like it is vibrating in the engine because you can hear it and feel it.
The quad is totally stock and starts perfect and runs perfect. Lots of power. Oil was changed regularly and is full. Have never adjusted my valves and the valvetrain does not sound noisey when running. Clutch is stock.
The quad has ran perfect since I got it a year ago and the problem has just come up the last few rides.
I don't think it is the rev limiter because I don't think I'm reving it THAT high.
The problem is hard to describe here so please let me know what details you need that I have not given you already to help me diagnose this annoying problem.

Thanks,
Keith
Marion, NY U.S.A.:(

[TM426]

Its probably nothing in the motor. Check your skid plate for the swing arm and go over all your bolts to make sure they are tight. ;)

[ghak99]

I agree, if it is a loud noise check all the bolts, we had a swingarm skid come loose and rattle one time. It drove us in circles until we finally realized it was nothing inside the motor.

If this is just a small vibration/rattle it might be nothing to worry about. I have only rode 4 or 5 stock 400ex's, but I thought they all had a vibration/rattle in them when pullling through the upper rpm's.

[400ex men]

go over all your bolts to make sure they are tight

[2001-400ex'er]

i have the same problem, i checked everything untill one day I was at the track and my skidplate was draging behind me and then i looked at the header and i was missing a stud... well opps and il look there first next time...:(

[KY Woods Rider]

Check the motor mounts, muffler mounting bolts, and the headpipe guard.

[400exdad]

To me, the 400 is not the most well balanced motor. I would look at the frame skid. I used some foam tape between my skid and the frame to help out. You may have bent yours and now its close enough to the frame to vibrate now.

[rr4406pak]

NEW DEVELOPMENT ON THIS PROBLEM!

I was going riding the other day when my 400EX would barely start. Then it would not start at all!

I switched over to reserve and it started right up!!! What the hell? (Even on reserve I still had high RPM problem)

Maybe I got some crap in the fuel line?

Could this be what is causing my high RPM vibration and loss of power? Maybe because my fuel line is somewhat plugged and starved for gas it is leaning out at high RPM and the vibration is just the motor starving for gas???

Has this happened to anyone before? I wonder how the hell crap could have gotten in my fuel line. It is a closed system for cryin out loud!

I'll keep you posted on what I find whenever my wife lets me out in the garage to take apart the fuel system.

Any opinions/suggestion are appreciated!!!