rejet with filter?

[400Rider022]

i have a k&n that i got for free and i want to throw it on but im wondering...do i have to rejet? if i dont will i notice any difference then if i did?

[F-16Guy]

Probably not. If you did a filter AND a pipe, then you might have to go up a size, but with just a filter, I'd keep it stock. You could always buy a 150 main for a few bucks and see if you like it, but I'm not sure there would be any improvement.

i disagree...the stock jetting is lean to begin with...you are adding quite a bit more air into the already lean mixture with the k&n and therefore you will need to rejet. you may or may not be able to gain what you need through your a/f mixture screw...do some plug shops to see, but don't over do it...lean is bad...

read this... jets r us (http://www.jetsrus.com/FAQ_jet_kit.htm)

[F-16Guy]

I added a filter to my wife's bone-stock 400ex and bumped the main up to a 152, and it was way rich. I went down to a 150, and it still didn't feel as crisp as the 148. The filter may potentially allow more air in, but if you don't open up the exhaust, the engine is still restricted to flowing that amount of air. I'm just speaking from my own experience, and I agree that it wouldn't hurt to buy a 150 and a 152 and give them a try. I'd even suggest throwing in a 40 pilot so it's not so cold blooded in the morning. It's only a $10 investment, and if nothing else, you learn a little about how your carb works. I just don't think he's going to see any improvement.

improvement not...not causing damage to the engine...yes...a lean engine will run better than a properly jetted engine...until it dies...

[puTTs]

I'd say put it in, ride for 10-15 minutes, then check the plug. My 05 runs a tad on the lean side stock. Checking the plug is the best bet, unless you have an oxygen sensor, battery and a digital rich/lean gauge laying around.