John---A few of us are working on the cause of this stumbling and
backfiring. It's too early to give a reason for exactly what is
happening, tho I've been able to correct the symptoms of this. I always
like to know why things improve, especially when deviating from
standard. Early indications are that the spark is out of phase, and
jumping to the tower of least resistance.
Meanwhile, "leanness" is just one cause of a misfire. There must be the
proper ratio of air and fuel to start combustion, and the spark to
initiate it. (No new news here) Generally speaking, if there is a
hesitation, and then a backfire with accompanying black smoke out the
exhaust pipe, the cause was interruption of spark on one or more
cylinders. The black smoke being the result of the second, or more, of
fuel intake strokes before it finally ignited.
You didn't say which way you "reset the timing" when it seemed to
improve.
Going "up a hill" always puts more load on the ignition system as
cylinder pressures increase thru larger throttle opening.
Be sure there's oil in both dashpots.
Let us know if and when you resolve your particular issues here.
Dick
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