This issue really fought me for a long time. I ended up installing a Dyna electronic ignition and new ignition coils/wires/caps. That helped with the backfiring, however it still wouldn't run just right. The #3 intake tube was forming condensation when running on choke and I never could find any issue with the carb or valves or timing. A Goldwing carb expert that I went to thinks there was an internal crack in the carb casting. In the end he replaced the #3 carb body and it ran perfectly.
Did you happen to get the answer ? Was it valve clearance?
This issue really fought me for a long time. I ended up installing a Dyna electronic ignition and new ignition coils/wires/caps. That helped with the backfiring, however it still wouldn't run just right. The #3 intake tube was forming condensation when running on choke and I never could find any issue with the carb or valves or timing. A Goldwing carb expert that I went to thinks there was an internal crack in the carb casting. In the end he replaced the #3 carb body and it ran perfectly.