If there was anything dumb about the "dumb but important" original question
on dieseling, it was the implication that the timing should be set so as to
control dieseling. The responses so far seem to buy into this concept,
but, in my (not too) humble opinion, the timing should be set to the
optimum value for a running engine, not set to accomodate the few seconds
after turning it off.
Having the ignition timing too advanced can promote dieseling, but
retarding it beyond optimum is not the way to cure it. If dieseling is a
problem with the proper timing, do something else to control it. When I
had this problem in my '63 B (it's periodic, depending on the state of the
engine), I adjusted the idle to be so slow the engine would stall. Then,
when running, the idle speed was kept higher by pulling the choke out a
bit. If properly adjusted, the choke affects only the idle, not the
mixture, for the first ~cm of its motion. Pushing the choke in just before
turning the ignition off became automatic to me and cured the dieseling.
For some years before fuel injection took over the auto industry, a
solenoid that automatically did just this was common on new cars.
Alternatively, one can slow the engine by letting the clutch drag a little,
with the trans in gear (and brakes on), before turning the key off. This
slight load will kill the dieseling.
Russ
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