Just my .02. . .
Have to join the "a bit of popping on decel is normal. (and KNOW that some DON'T) Mine's (carb)ega/dyno setup, and has always done it (always had slip on free flows (Kerker) and stage 1 a/c).
Did observe during a trip out west, that my left pipe, which had alway been fairly cool, burned me when I relaxed my hand down by the seat during a trip out west, extended high speed riding. From that, think the left does get used during the higher speed runs, just not much for all the "normal" urban/suburban type riding??
Rode a loaner FI Heritage not too long back with SE stage 1 pipes - it had no popping, but then, for some reason, (I hear it's not normal) the bike had no decel. Somehow, the FI only let it back off very slowly. LOL - no decel, no popping.
Good rides,
RainRider '02 FLHT