i have a 04 400ex, white brothers e-series slip on, stage 1 cam, kn, & jetted. My question is will it hurt the bike if u take the spark arrester off

 

if you ride in parks where they require some sort of arrestor then yes, but otherwise no...

 

Your spark arrester is so if sparks come out of your pipe the sparkarrester is a screen so it blocks the spark from coming out and starting a fire. It may even run better without it. It won't hurt anything. I would keep it in when u're riding in grass and trails. I wouldn't use it in the sand and when it's wet. Most places require it though.

 

I'd take it out, I have never seen a spark actually come out of one and land on the ground, maby a flas out of the back 6 inches....but never a "spark" that had potential to start a fire.

 

me too.