Motorcycle Repair: 2002 XL1200C Backfire through Carb, plug gap, rear cylinder

Question
Good Afternoon Mike,

I have acquired a 2002 XL1200C that has developed a backfire through the carb.

This bike has a Sampson Caliber 2 - 1 exhaust and a Screaming Eagle Stage 1 air cleaner kit.

When the backfiring began I pulled the sparkplugs.  

One plug was fouled/black (rear cylinder) and the front was clean, no oil fouling on either plug.

Minimal amount of oil through the oil cleaner at the present time.

Backfiring mainly at idle.  Cruising speed no problem.

Dealer had rejetted this bike in 2003 and exhaust and SE air cleaner kit was added in 2006.  No problems in 2006, 2007 and 2008.

Is this a plug gap issue, bad wire, bad coil, does the carb need to be rejetted.

Please advise.

Dean

Answer
I would doa OHMs test on the coil and plug wires. That can cause your problem. Also, check for a intake manifold leak. You can check it by spraying some carb cleaner around the manifold and it the RPMs go up you have a leak
Good luck and happy riding
Mike