She has a 2000 400 ex, it has a HMF slip-on, K&N filter, and a open airbox (no lid). It also, 70 degrees out and we are at sea level. At just off idle it burbles really bad and blows black smoke. Main jet is a 170, airscrew is at 3 turns out and the needle is at three notch up from the bottom. It runs really good threw the mid and top end. Any help would be great.

 

Did it run good before, and this is something that just came up??? If so, sounds like something clogging a jet.

Or did you just put on the pipe, etc., and you don't yet have the jetting quite right???

 

I just put the pipe on, and started to noticed the black smoke.

 

So you attempted to rejet for the mods??? (I can't remember what the stock jetting is.) If not, you have been running lean, and your engine may be toast.

 

Black smoke usually means rich. When you make a change to the intake/exhaust system you have to make changes to the carb. Changing the pipe allows more air which usually gives you a leaner mixture, but that sounds opposite of what your experiencing. This should explain everything you need.

 

Killer site! thanks. Im thinking the quad is running fat and I need to adjust the air/fuel screw.

 

Well if you haven’t touched the jets I would. A screw isn’t going to do anything you need to rejet if you haven’t.

 

allready rejetted it. going to try to reset the airscrew to 2 turns out.