So started bike this morning and set off. After about 50 meters she started to backfire and struggle. After another 50 meters she dropped down to a single cylinder. I turned around went home and checked the plugs etc. They both had a strong spark but the rear cylinder is not firing. Had to leave the bike and get a taxi to work. She was running fine last night and never missed a beat.Any ideas before i start tearing her down. Thanks Oh and she is a 2004 883c

 

Spark at the rest plug.. Not firing in the rear cylinder. Assuming you have good compression in that cylinder, then I say you are not getting fuel.in that cylinder.

 

If you've got spark, check the wiring to the fuel injector. Been known to fail just like that. Takes something pretty catastrophic to kill compression to where it won'tfire, so its probably a fuel injector problem.

 

I don't think fuel injection was available on the sportster before like 08. is the plug wet or smell like gas? I went through similar symptoms on my street glide but mine was because an adjustable push rod backed off an wasn't opening the intake valve.

 

My ex had a bike that did something similar. Turned out the genius filled the tank with diesel.