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Vibration.
Vibration.
I think you may be on to something ... being a tad hard of hearing (no not the Harleys' fault, 20 years in Naval engine rooms), it maybe the less vibration that makes it "sound" quieter. It is way smoother. On my daily therapy (my ride) today, I will try to determine if it is just a smoother power generation or really quieter. My guess is once again Kevin has hit the nail on the head. Amazing how just a little different fuel to air mixture can make that much difference. Guess you can teach an old dog new tricks.
Sorry for the short responses earlier...super busy.
When a tune is in the sweet spot (like the one you really worked on a few years ago), then the engine just hums. It has just the right afr and the spark is getting there just at the right time to keep things moving smoothly....spark getting there a little soon or late can cause very minute hesitation...nothing you would feel on acceleration, but something that would cause thousands of very small extra vibrations per minute.
When a tune is ok, but not in the sweet spot, there are hundreds of little pieces in the engine, trans, primary (and rest of the bike) that will all vibrate a little more. This equals more engine noise and a slightly less smooth running engine. (rocker shafts, primary chain, etc.)
Kevin
All will shorten the life of the engine
Sounds like you and Kevin have a close to perfect tune
I hope the new O2 sensors behave them self's:clapping: