I have a 2000 400ex and its only 6 months old. Its doesnt smoke bad but it burns oil quick. The shop said i have excellent compression. Do you think it could be somthing with the valves.

 

Unless you've sucked dirt or something similar, use a heavier grade oil. Air cooled engine run hot and break light weight oil down quickly. I run 15w50, it cleared up my smoking problem.

If you want more info, do a search, myself and others have posted much info on this topic.

 

I run Mobile-1 tri synthetic 15w-50 and run Exxon 93 octain (best oil and gas companies do some research) if this doesn't stop it get someone that knows what they are doing to check your exhaust valves. It should use a little oil and blow a little smoke for a second when its cold (first start of the day) try the oil and gas for a little while and see how that goes.

 

I have the same problem. Mostly smoking. For example, I'm goin in 3rd, shift into 4th and give it a handfull of throttle and it puffs white/blue smoke. I run honda 10-40 oil, change it regularly, clean my filter regularly, and broke it in properly(slow and easy). After break in I got my valves checked.(over a year ago) My dad said it could be the exhaust valves os guides(I thimk that is what he said) but I thought I may have to replace the piston and rings. Will it help if I run 15-50 oil in the summer(to thick for winter)?

 

Wicked400exoes your clutch slip with the synthetic oil? I heard it is not good for wet clutch atv's. If it doesn't hurt it please tell me. My 400ex smokes a bit and goin to 15-50 from 10-40 may help. I want to run synthetic, but want to make sure it doesn't hurt my clutch.

 

I TRIED THE SYNTHETIC OIL BY MISTAKE AND IT TOOK 3 OIL CHANGES BEFORE MY CLUTCH STOPPED SLIPPING. STAY AWAY FROM SYNTHETIC IN A WET CLUTCH 4-WHEELER

 

guys I race motoX if my clutch slipped i wouldnt use it. my engine is stock honda oil filters stock clutch and all No Slippage my friend uses it too with a 440. call Mobile and ask them about it and see what they say! or goto their web site

 

dont know about 300ex. your clutch slipped? u mean you would go and then it wouldnt and then it would grab or the engine would rev higher but u wouldnt go faster? thats slipping. is that what happened? what oil and grade did u use?

I heard things too, but mobile1 15w-50 works fine for me no smoke no slipping