I have an S&S 113. I know its not Harley but I need help. It fire intermittently on the rear cylinder. Not so much at low rpm, it will kick in at higher rpm and still pull hard. Thought I felt the exhaust kind of sucking in on that cylinder at times. Single fire ignition, coil seems ok. got new plugs in, plug wires on the way. What else should I look for? Thanks all..

Tommy