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Hey - in the epic (and now closed) "diagnose my bike" thread, you mentioned that with the airbox off you were seeing something that looked like ignition happening in your TB - this gave rise to suggestions that included bad cam timing and arcing from an injector, among others.
A few days ago I was running my bike with the airbox off, and I had disconnected the vacuum line to the petcock from the rear carb. Not surprisingly, I was getting a bit of backfiring from the lean condition on the rear carb - the same kind of cough/sneeze/hesitation you hear at idle on a cold day when the bike needs more choke after starting. I also clearly saw the same kind of phenomenon that you described in your thread.
I would have liked to add this info to that thread, but it's closed. I don't know if it helps you, but I wanted to share in case others were as perplexed as I was about what you described. It appears that this is symptomatic of a vacuum leak or lean condition, not the esoteric stuff proposed in the big thread.
A few days ago I was running my bike with the airbox off, and I had disconnected the vacuum line to the petcock from the rear carb. Not surprisingly, I was getting a bit of backfiring from the lean condition on the rear carb - the same kind of cough/sneeze/hesitation you hear at idle on a cold day when the bike needs more choke after starting. I also clearly saw the same kind of phenomenon that you described in your thread.
I would have liked to add this info to that thread, but it's closed. I don't know if it helps you, but I wanted to share in case others were as perplexed as I was about what you described. It appears that this is symptomatic of a vacuum leak or lean condition, not the esoteric stuff proposed in the big thread.