The headers get really hot no matter what, but hotter when going slow or in low gear. If you know someone with a thermal infrared temperature meter, you can shoot the headers to see how hot they are actually getting. Or you can check the spark plugs to see what color they look like, but that may take a while to get a good read. You could throw a shim under each carb needle, and go up one size on the main jets to see if there is a difference. I agree about the float levels in each carb as well - set a little low level, and it would lean out the mid to WOT range. There's so much more to check too. I have another buddy with a 2012 going through overheating issues, but he has not got back to me about it.
05 750,Stock Engine,Muzzy Pro Exhaust, Uni Air Filter,
14" Vision Bruiser wheels, 26" Kenda Bear Claw HTR,
3" PVC Intake w/restriction - 2" ABS CVT, center snorkels,Carbs Keihin-#40 pilots 2 1/2 turns out A/F ,#158/#158 mains w/30 thous. washers under stock NFKL needles, 2012 front suspension,
Mr. Gasket 42s Fuel Pump Mod
10" Hayden s-type Electric Rad Fan Mod - mod fan mount
Aftermarket ebay radiator