Put a K&N air filter on my trx250 this afternoon really ran like crap at first had a really bad lean misfire at 3/4-wo throttle had to go 2 main jets bigger and raise the needle one to get it to smooth out . My mechanic friend stopped by and suggested that I take the crankcase breather hose off the air box so the motor could breath better and stop drawing hot air into the motor and more cool air. I was not to sure about this working but hey why not try it ? So I blocked off the air box hole ran the breather tube under the gas tank and tried it the only thing I noticed is that I had to turn the idle down a hair and over the same section of road it was about 2 seconds faster after several trys with differant riders Now after everyone has gone to sleep reading this my question is will this hurt anything leaving things the way they are I don't think it made a big differance but it did make a differance

 

If you don't have a filter on the end of your crankcase breather tube you will suck dust and dirt into your engine. Also its better to maintain a vacuum on your crankcase or you may burn more oil.

 

http://motorcycleinfo.calsci.com/Fil...tml#OilFilters

Read the air filter article (top of the page)! I just don't trust those things!

 

Well now I have read that I don't know wheather to cry or laugh I have K&N's in every thing I own , 89 jeep xj ,2000 suzuki vitara, 95 gmc van, 2004 trx250 and 2005 suzuki lt160

 

Many people have been using them for years without problems. Everyone I know, including myself, run Outerwear pre-filters outside of them to be on the safe side.

 

I ran K&N for years with no problems too (that I know of), but a UNI flows almost as freely, and with way more security, so why take the chance??? I would run one on a street vehicle, however.