400EX can't rev high? Why?

[rr4406pak]

Hello Exriders,
I have a stock 01' 400EX that I have a big problem with.

At high RPMs I lose power and get this massive vibration in the motor (almost like a violent harmonic resonance). Why? :confused:

It is not because of lose exterior bolts (like skid plate, motor mounts, etc. I triple checked). At low to mid RPM I have plenty of power and all is fine.

When I first bought it it did not have this high RPM vibration. Everything was fine.

It is not overfilled with oil.

I have not checked the valvetrain or attempted to adjust the valves.

One strange thing that happened is that when gas knob was set on "ON" it would not start. When I turn it to "RESERVE" position it starts up and runs fine (BUT I STILL HAVE THE HIGH RPM VIBRATION). It is clear that some junk has gotten into my gas tank/fuel lines and is blocking up the works.

Is it possible that the engine is starving for fuel at high RPMs due to a blockage??? :huh Would that cause the strange vibration/loss of power???

The vibration feels bad like something is going to break inside.

I do not race. I can still ride this thing very fast but I can't push it like I should be able to.:grr: What fun is that?:(
HELP!:mad:

[khen]

You might want to check your main jet for any blockage and also clean out your carb, lines, petcock and tank. Sounds like it could be leaning out and missing.

[zephead400ex]

I had the same problem with my quad not starting w/ the gas "on" but would start w/ reserve. Check the petcock, probably dirty or clogged.

Check your main jet, could either be loose or clogged! If it's clogged, you probably have bigger issues too.

[mojoe2878]

i would try removing the carb and gas tank and cleaning them both real good, be sure to remove the petcock on the tank and clean it also.
clean the plug or go ahead and replace it since their only a couple dollars, be sure the air filter is clean too.
then adjust your valves.
it probably just needs a good tune up, it sure wont hurt nothin.

[rr4406pak]

Bump

[Destructo]

I have a Vibration on my 01 400ex also, more so than our 99 Fourtrax 300, but I have never owned one of these before, i'v been riding a 85 XR200R for the past several years and it runs smooth. But my 400EX seems to have much more vibration than anything else i'v ridden, but it sure seems to have a lot of power and I don't run the rpm too high very often but doesn't sound like its missing or anything.

I pulled the body work off to fix a front mounting point and noticed the air filter is quite dirty, so i'm going to try giving it a good tune up.

Mine starts and runs great on the "on" position and idles and seem to run out fine but never ran the rpm too high.

I just bought it this week.