I have a carbureted, 2000 Heritage Springer, modified to a 107 ci CNC ported Screaming Eagle head and a Screaming Eagle Mikuni carb. About every other time, when I shut it down, I get some kind of spit, or coughing back thru the high flow cone air filter. It is kind of a exhaling sound. Sometimes it is loud, other times not so loud. Sometimes smoke comes out the filter. What could be causing this?

 

Unburnt fuel igniting from hat not spark with an open intake valve.
No clue how to fix it though.

 

I'd check pushrod adjustment if you have adjustable ones. Maybe timing? I'd think it'd run rough though.

 

I have S&S Quickee pushrods. I have checked their adjustments, and they are up to specs, set at four turns. The bike runs great at all speeds. I do have Dynatek re-programmable electronic timing, but I know nothing about it, and I am hesitant to mess with it. The sparkplugs are all full of black soot. Does that indicate it is running rich? One thing I did notice, is that recently, gas has been dripping from the carb's plastic drain hose onto the ground after I shut off the engine (with gas valve in off position). I suspect the carb float and/or needle. I think I will be taking it to an indy shop to have them take a close look at it.

 

Sounds like a timing issue.
Scott