I've recently added a K&N filter to my Trailblazer but do not have the airbox lid off. Am I now required to re-jet? I've always assumed I would have to do that if I also added a pipe.

 

You shouldnt have to with just a filter but I would run it then check the plug to be safe.

 

With any intake or exhaust change Jetting needs to be Adjusted.

Chances are with just the K&N you will be fine, Polaris starts them out on the Rich side (Good for break in).

Keep in mind also when it gets cold (Probably doesn't in Arizona) Jetting will need to go up. I think they recomend a Jet change every 20 degree change in temperature. Jet up cold, Jet down with warm temps.

Just another piece of advice for a new K&N owner, Keep it well oiled. I was told by AAEN performance that they rarely see and engine fail due to lack of engine oil or oil injection. Most are from guys letting there K&N run dry, witch allows fine dust to go right on through, witch can destroy an engine in a weekend of riding. You may want to invest in an outerwear for that filter also.

 

in general k&n air filters flow 20-25% more air to the engine than stock,so they lead the motor more toward the lean side jetting,on a stock
engine you should be ok,but just take a look next ride to be safer.