I had the same problem with my '99 400ex. It would run strong on the low end and cut out on the top end. I run stage II and am about 400ft. With screw out 3 1/2 and clip on 3rd position, the kit called for the 146 main. I was running rich and called Gary at Dynojet last week and he suggested going to the 142. I changed it yesterday and it made all the difference in the world. You should blow away a stock 400ex so I think you may need some fine tuning. Call Dynojet and talk with them. Also look at the info that came with the kit because it may help you decide if you are lean/rich. Good luck.

 

(bshiels) you better put in a new spark plug and
run it then check the plug, if you were'nt fouling
plugs with the 146 then putting in the 142 you might be to lean, a bike will run real good when
there lean. just thought you might want to now.

 

(bshiels) you better put in a new spark plug and
run it then check the plug, if you were'nt fouling
plugs with the 146 then putting in the 142 you might be to lean, a bike will run real good when
there lean. just thought you might want to no.

 

Thanks, I'll be sure to do that.

 

This is probably a stupid question, but where is the air/gas screw on the carb? I am waiting for my shop manual to come in, so I'm not sure. I think it's the screw on the left side, just above the choke lever...