I have an 04 1200 custom that just recently began backfiring after running at highway speeds. I will pull to a stop and the engine begins to stumble. If I wrap the throttle she will backfire. If I hold the RPM up while stopped it smooths out. I had her at the dealer for a week and they claim they could not duplicate the problem. I picked the bike up tonight from the dealer and as usual ran fine while warming up and at highway speeds. First stoplight...shooting flames. I have vance and hines pipes and have put in a stage 1 kit in the carb. Any ideas? Only happens when she is warm.

 

You need to get that bike back to the dealership asap. Tell them that it starting shooting flames and it will be fixed quickly. If not, then call harley headquarters and tell them that your bike is shooting flames and how that's a SAFETY risk. Keyword there is safety. When your safety is compromised and then they know lawyers will tear them apart if anything happens and things get fixed quickly.

 

Hell, I say leave it! I'd love to be able to shoot flames... Cool!

Hope HD gets the problem fixed for ya. My very primitive mechanical knowledge says that part of the problem could be your bike running rich. (?) Is it possible for excess gasonline not to be burned, but instead pushed out the exhaust port???

 

Its timing or a valve problem.

 

I agree it's a valve or timing problem. Becuase it's only happening after the bike is warmed up and you are at idle, and you're not complaining of performance problems. I would say the ignition is retarded too much at low RPM. This could cause the exhaust valve to begin to open as the ignition fires. Increasing the RPM would temporarily stop the problem. Get it fixed quickly, exhaust valve seats are not designed to operate in a fire bath.