I have a 2005 sportsman 500ho that is putting out 12.5v at idle and 17v at 2000-3000 rpm it also misses and blows out black smoke when i rev it up and sometimes shuts off. I have done a lot of work on this atv recently and was wondering if the ECM would cause both problems? My atv has the SurePower ECM. Starts and idles good problems seem to get worse as the voltage goes up. Thanks in advance for any help.

Recent Repairs

New piston rings
New air filter
New carb
New spark plug/wire and cap
New battery
Rebuilt starter new solenoid
Checked camshaft for wear
Checked and cleaned fuel pump/fuel lines new fuel filter
Checked throttle kill switch
Checked has steady white spark