> Looks like the first - when the choke is pulled more and longer, there is
> much more power, but then the engine roars heavily @ 1500+ RPM when you
> for the first traffic light.
Ah, mixture then. Do you have K&Ns? Could be the needles.
> The backfiring also occurs when the engine is running at "normal"
> temperatures and the outside temperatures are at freezing level or lower.
> How should I correct this?
> Is the vacuum advance timing involved in this?
> How should I check the vacuum advance mechanism?
Is it backfiring in the exhaust after a missfire? If so that sounds like
ignition. Is the tach fluttering at the same time? If so ignition LT, if
not HT. If the backfiring is occuring at a steady speed and throttle
opening then I doubt the vacuum advance is involved, but a changing throttle
opening altering the vacuum can affect the ignition LT as previously
described. Testing the vacuum advance is easy with manifold vacuum - just
point a timing light at the crankshaft as you pull the pipe off the carb and
the timing should become less advanced by the figure appropriate for your
capsule. Ported vacuum is a little more difficult, I watch the timing
whilst I suck on the vacuum pipe and watch for it to advance. Not easy to
get maximum advance without a vacuum pump, but generally they either work or
they don't because the diaphragm is split, in which case it won't hold a
vacuum and you can keep sucking air through, which weakens your mixture -
see problem No. 1!
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