I recently rebuilt my 2007 Nightster engine. Broke it down and replaced gaskets and what not. After reassembly it now idles rough, and at low RPMs sputters and runs terrible. At moderate to high RPMs it smooths out and runs fine basically if you roll the throttle slowly the first 1/3 of throttle rotation it runs rough. What could it be?

 

Lots of backfiring too at low RPMs, running almost as if I hadn't put the stage1 tune on it but a little worse

 

Seems like exhaust or intake leaks are a good place to look with a new installed EFI. Without a carb, it's that, or one of the sensors may not be connected, faulty, or your ECM needs some resetting or adjusting.

John

 

^+1, especially the intake leak.