i've just been noticing this lately. My ex has had a k&n on it for 2 years and now it is just starting to show signs of damage (smoking).

 

You will never see a K&N filter in my quad. Rebuilt to many quads with low miles on them with K&N filters in them.

 

YOU HAVE TO KEEP IT OILED!!!! or get an outerwear cuz if you dont properly maintan it, YOU WILL RUIN YOUR ENGINE!!! how many ours do you have on your quad? my 400ex is only 2 years old and it burned oil when i bought it even though it had the stock filter and airbox lid, maybe its just that400ex cylinder bores just dont last, i dont know if its just because my quad was so brutalized but im very unimpressed with the quality of the fasteners, shocks, connecting rod, plastics, cylinder bore, valves, cam, bearings and transmission. what does everyone else think?

 

Sounds like someone put a oil filter in back wards. When you do that you get to do (connecting rod, cylinder bore, valves, cam, bearings and transmission) It all goes real quick with a dry sump motor.