I have a 6 month 400ex Honda , all stock except for uni air filter. I off road ride in woods and sand pits. Regular maintenance (oil change, air filter,plug,schedule valve adjustment performed). Problem: Exhaust ( white smoke, medium strengh in color, only when given gas, not when starting and idling, Honda dealership states good compression). Taken in for 6 mo. Factory warrenty check on smoke problem. They clain they can't goe any further due to dust residue in air tube. They say Honda Factory says dust or dirt negates warrenty. They would have to charge us $300.00 plus dollars to look into valves. They (honda dealership) say it is probably a valve problem (their educated guess). You guys out there, can you help us with this problem? Hondas not. Any help would be appreciated. Thanks.

 

Are you looking for monitary help in fixing the problem you caused buy messing up the air cleaning system? Buck up for the over-haul and be more carfull in your choice of aftermarket parts... How does that taste?
Or, just put thicker oil in and hope it goes away, that is what "we" did...

 

It's the nature of the beast. If it smokes alot there is something wrong, mild smoke is the nature of the 400EX. If you have alot of dirt in the intake throat better get a better air filter or seal it up better. Forget K&N for they will allow alot of dirt to get through.

 

My K&N sucked in a little mud once and mine smoked a little, got much worse and I had to get new rings so I decided to reeplace piston and sleeve too, that how I got my big bore. I'd say your ring are worn out, dust is very abrasive, like sandpaper to your ringsd, good luck!