I have a 2004 HD Road King Custom that I recently added a Big Bore kit, cam and power commander module. I have approximately 200 miles since upgrade. Started bike the other day and it began to idle at more than twice normal rpm. Not being able to slow the idle, the motor back fired 4 times out of the forward cylinder and severely darkened the heat shield just inches out of the cylinder. Shut the bike off immediately and am waiting to take to the dealership that did the upgrade but was wondering if anyone could give me any information as to what might have happened. I've had no problems before this happened.

 

Sounds like what I had in a '96 Ultra one time, turned out to be a short in one of the wires for the fuel injection to the rear cylinder.