This may seem dumb, but I'm kind of new to working on my quad (2000 400EX). I had a guy rejet the carb with a Dynojet kit on Saturday, April 22. I rode it a little before I had to leave. It bogged down for a second or two every once in a while. This made me think that I was getting to much fuel and not enough air. Then, I discovered that black, un-burned fuel was coming out of my Mega Max II silencer. That confirmed to me that my 400 was getting WAY to much gas and little air. M question is, how hard is it to adjust the fuel/air mixture screw? Which way do I turn it? Is it easy to get to? Where is it at exactly? Forgive me for asking a dumb question, but PLEASE HELP!!!

 

Where does it bog? at 3/4 to full throttle? If so, its not your mixture screw its your main jet. Your running too rich. Just keep dropping one size at a time until the bog dissapears,and the plug is a nice tan/light brown color. The mixture screw meters the idle circuit, and doesnt affect anything in the upper throttle ranges.

 

I would hate to ask the obvious but did you at least open up airbox and install better flowing filter?