necessary to rejet

[Buck Naked]

I just got my HMF slip yesterday. I installed it and went out for a ride. There was no breaking up on top, no backfiring on decel. and the header is not glowing. No signs of improper jetting. Should I rejet it anyway even though it seems to be running great?

[Brehmmotorsport]

if you are still running stock air box with lid and stock filter then you shouldn't probably don't need to rejet. Just check you plug to be sure though.

[400EXtreme]

I didn't have to rejet but do what he said and check the plug.

[exboomer]

What's the point of opening up the exhaust if your not going to allow more air and fuel? You should re-jet and either modify your airbox or install a better air filter.

[Buck Naked]

Whats a good starting point for jetting. I think my pipe came with a 152 main. I plan on throwing it in sometime next week and see how she runs.

[Brehmmotorsport]

not everyone wants to get more air flow. A better slip on pipe makes a very big difference on a machine like a 400ex. Maybe not so much on a dyno scale but the throttle response and quickness cannot be denied. As far as your jetting 148 is stock so a 152 is a little richer and if you can push it with the air flow you got now go ahead and use it. Jetting is different on every quad. I have stock motor but run a 170 in mine. I however run a tc shorty and have a k&n with mod airbox lid. I would check your plug if you are lean go ahead and put the 152 in.

[Buck Naked]

What am I looking for when I take out the plug.