ATV started smoking...

[FoxHondaRider]

Yesterday my 400ex started smoking when it was hot from hard riding.  It wouldnt smoke until the engine got pretty hot and if I let it sit a half hour or so and ride it there wasnt any smoke until I started rompin on it.  Then I shut it off to let it cool down again and a small trail of smoke was coming out of the exhaust when the engine wasnt even running!  So whats the deal here?  Bad piston rings make it smoke all the time so that cant be the cause, valve seals would make it smoke all the time too so I dont think that would be the cause, my muffler packing seems to be good... why is it only when its pretty hot it smokes?  Its only when you hit the gas fast not so much slowly going on the gas up to speed.  Another thing to add it was like a whitish/ little bit of grey smoke it seemed.  So whats the cause?  Anybody know whats going on?

[quadracer1992]

This may or may not be a stupid question, but does the bike have oil in it? I ask this because someone i know was wondering why the bike was over heating, and when he checks the dipstick the oil is bone dry.

[Turboderf]

time for a rebuild

[trx#9]

Rings probably. Is it pushing out any oil from the vent tubes, like the one going to the air filter box.

[FoxHondaRider]

I just came up with an idea dont know if it sounds logical or not but it does to me.  I cleaned my K&N and oiled it maybe 3 hours before riding.  Could it be that there was excess oil being sucked into the motor only when in high RPM racing which the intake flows most and sucks more and obviouly the motor being hotter from racing like that.  And it smoking after racing it hard even when the motor was shut off from the K&N air filter oil burning in the headers?   The motor never lost power and it ran great its just when I would really romp on it racing it hard it would start to smoke when i would rev the motor quick.

[trx#9]

Take the filter of and check the boot for oil. Unless you drench it i dout its oil from the filter.

[family fun]

i have an 05 400ex and i had the same problem but i determined i had a little bit too much oil in the motor as soon as i drained it and had about another hour of ride time on it i never seen it smoke again that was about 8 months ago and i'm still riding it pretty hard

[FoxHondaRider]

mine was too little oil or something.  I just changed the oil and it hasnt smoked since.

[Fox17]

i was riding my XR400 (same engine) and it lost power and poured smoke out the pipe. it still smoked for like 15mins after i shut it off. it had bad rings. i let it sit for a few and it started right up and quit smoking the whole ride back to the truck. i did a rebuild and im waiting on one gasket and ill be good to go. idk what could be wrong if it had all power and ran fine. how much smoke is coming out?

[crom A zone]

just make the vavles chater and make alot of noise and say it is a desil engine thats what i do lol   it sounds like you need top end rebuild my freind

[FoxHondaRider]

I heard it could be overheating.  I had a low oil level like barely on the dipstick.  I changed the oil and ran a thicker oil (20w-50) because its always hot in the sunshine state.  Ran it twice at Croom like I normally do no smoke ran fine and it didnt seem as hot.  The motor wouldnt get as hot and it would cool down quicker.  So I think the low oil level made the oil heat up so much being 10w-40 and it would overheat.