ok, heres the problem.. buddy of mine got an 85 FXRP. stock carb on it and as far as i know stock pipe. he starts the bike and starts backfiring out of the pipes when he hits the throttle and when hes cruising it pops on him and makes the bike jump.. any idea whats causing this? im thinking his mixture is off... maybe manifold leak? any helps appreciated.

 

Sounds like electrical, check all connections from the battery to the ignition and don't forget the grounds. What was done to the bike before this started? How do the plugs look? Hope this help, let us know what you find.

 

guy bought it from his uncle, his uncle went down.. tried to fix it.. i think the bike was rewired, new stock heads were put on.. didnt pull plugs. lookin for some ideas for him to check an try an figure it out

also, shoots flames when it backfires out of the tail pipes

 

Check the battery connections including the grounds first, I am not sure, but I believe there should also be a flat braided ground from the frame to the engine also as it is a rubber mount and the engine is not grounded well without it.

 

cool, will check it out

 

does it diesel when he turns it off?pull the points cover and look to see if any thing is melted

 

I had an old shovel that did that... the timing plate was loose.

 

Might be sure the exhaust is sealed at the head - if it is sucking air in and the mixture is rich, the exhaust gases can ignite from the heat.

 

could also be a combination of running way too rich with either an exhaust leak or some type of air leak

 

my bike did that i had a manafold leak. start the bike get it to an idel take some carb cleaner spray all around the intake if it kills the bike its leaking. also after i found my leak after awile it started agin i had a crack in my carb leting it suck air