I just worked on one of these last week.
Same issue.
Turn out the air screws. They are (or should be, if I'm right) underneat the carbs, on the head side (as oppsed to filter side) to 2 or 2.5 turns out, then let the bike warm up (ride at least a mile or 2), and adjust the idle down..
This is a short term solution. If the bike wasn't jetted after installing the kerker, you'll need to increase the idle circuit jet... I havent had one of those apart yet, but the idle circuit may not be removable. If thats the case, you can buy carb drills. drill them out half a size up. i.e. if they are 40's, drill em out to 45 and see what you get. Do not just go nuts. If 45 works pretty good, but still a bit lean, do no go 50, go 47.5 (or whatever).
The same may apply for the main jets. If I get an opportunity to open the carbs on the bike I worked on, I'll let you know what I see.
(Oh yeah, I think it's possible that these bikes run lean stock. It could be that they would all benefit from a rejet. They may be right on the ragged edge of lean stock, meaning, you cant really tell they are lean, but the smallest change dumps em over to '#$%*, this runs like crap' territory too easily.)
