1972 FLH, new plugs, new fuel filter and petcock, freshly rebuilt S&S Super E carburetor, new air filter... ran fine Monday, with the carb popping very occasionally, then sat for a day, started it up Wednesday, rode for about a half hour, the carb popping more often, and a little backfire through the exhaust, progressively getting worse as the ride went on. Started it today, and I can't even ride it, it's backfiring so badly through both the carburetor and the exhaust... I'm fairly new to this, and I don't know what could cause both like this. Any suggestions are appreciated. Thanks, - Danny

 

I'd start by checking for an intake leak.

 

+1 on the intake leak. Make sure your carb is supported and not just hanging off the intake manifold. If it is supported make sure tightening it up didn't pull the carb away from the seals.

 

Ran it, sprayed carb cleaner and wd40 at all the seals/clamps 4 times... nothing. No indication of a leak. Any other suggestions? My mom works at Dennis Kirk so I'm gonna call their Harley tech and ask him about it too.

 

Mine did the same thing when the ignition was on the way out.

 

Also, just pulled the dipstick, and it smells very much like fuel...

 

Mine also did that. It was loading up with fuel when the iggy dropped out. I've also had mine do this when the float needle was not seating.

 

I know you said you had new plugs, but I'd check them all the same. Sounds like possible fouling. If it's not, well at least you eliminated that possibility.

 

Mine was doing that turned out to be the points. Put in a new set problem solved. Pop off your points cover turn it over and see if the points are working that's how I found out on mine.

 

No points, electronic ignition.