My 400ex is one month old. When I push my thumb throttle and release it, as the rpm wind down their is a very high vibration coming from the engine. The vibration is so intence that it travles threw the engine, frame, Handle bars, and to my hands and arms. It makes riding very tiring and not fun! It also does this when I'm in neutral and standing still, so I would think that would eliminate the wheels and tires. I have checked all bolts and spark plug, all tight! It only happends when the rpm's are on their way DOWN I dont fill anything when I'm throttling.

No mods.
PLEASE HELP!!!!!

 

well I don't think there is something wrong with it but put on some aluminum and fill the ends with silicone. this is will make a big difference.

 

This is defiantly a engine problem! It started doing this after the first two weeks. Major difference in the bike now! Just overnite. It is so bad that the quad is almost unrideable! After about a Hr of riding.

 

If you have only had your 400 for a month or
so and you say the vibration is coming from the
motor I would consider checking the valve clearence. This should be done within about a
month after purchasing a new machine. Good luck
Santa.

 

Would bad valve clearance cause vibration?

 

Yes. And will also cause major engine damage
if not corrected.

 

man, thats deff the valves...get them adjusted and i guarantee you that will fix your lil problem....they might have been adjusted wrong from the get go or anything

 

why not take it back to the dealer with a complaint . it should not have this problem this soon if ever . besides has anyone thought of something being out of balance like the flywheel . hmmmm makes u think about vibrations & being balanced wouldnt u say .

 

Y don't you take it back to the dealer and see what is up... It is still under warrenty if it is only a few month's old..

 

DOES IT ALSO BACKFIRE WHILE DECELERATING? IF SO VALVES DEFINITELY.