I have a 2003 AC 400i, with a HMF exhaust . It has the quiet core and spark arrester installed. I have a stock 150 main jet in it, and i turned the air screw out one extra turn. The bike pulls good on low to mid range, but falls very flat in upper rpms. I tried jetting up one size 152 and it ran better, but the spark plug looked very sooty. I ride at low Elevation 700-2500' Any ideas an adjustments? Is a carb kit the way to go,or should I go back to stock? PS It has the manual transmission. Thanks for any help.[img]i/expressions/face-icon-small-smile.gif[/img]

 

Doing a plug chop, must be done right...or the plug reading doesnt mean much. Just go by the drivability symptoms, and youll get it right.
Dont bother with a jet kit...the piece of paper is very expensive...the jets are cheap.
Heres a good article on jetting yourself, and it lists the drivability symptoms to watch for.
Jetting
If its still breaking up, at WOT, then youll need to go bigger on the main.

 

Thanks for steering me in the right direction. It did run better with the 152 in it. I will put it back in and try adjusting the air screw and see where it is at. Thanks again