I have an 06 RK with SE air kit, S&S mufflers, and SERT with dyno tune.
4000 miles on this set up and bike runs perfect accept when accellerating hard,
I will get a slight pop or backfire between shifts. Is this a lean or rich problem at
this rpm point and do you think it's worth chasing this down. Like I said, the bike
runs fine as is, runs cool, no decel pop or backfire, pulls hard and gets
around 42 MPG as the average.

 

i think it's rich

 

Might be an exhaust leak.

 

Decel popping is normal I think but I would be concerned about backfire between shifting. Probably nothing major but I think I would have it looked at.

 

I agree with rich. Had the same thing with my Roadglide with a stage 1 tune with SE AC and Kerker mufflers. When I had it bored to 95 with SE 204 cams and added the performance baffles the popping was no more. I particularly noticed it before when I would idle for a while and then short shift to second it would pop out the pipes between the shift.