Mark---"Regular" motor oil has gone up several grades since our cars
were built. This should mean that it is better than what engines needed
to perform and give long service when the cars were designed. Based on
this, I personally wouldn't spend the extra dollars for the synthetic
type, unless your engine is being exposed to kind of treatment that
these oils were developed for. Some may say while they pay twice as much
per quart, but change the oil half as often, cost is a wash.
Generally speaking, "smoke" out the tail pipe comes from any of three
sources-- Water condensation, or steam (white), oil burning (blue),
fuel or carbon (black). Some black smoke while using the choke is not
unusual on startup. It should stop when the choke is returned to the
'in' position. The extra 500 rpm you're seeing suggests that something's
not returning to where it was. (Not necessarily a choke, but look here
first).
I don't think changing to the synthetic is part of the black smoke
sighting.
Dick
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