To my considerable surprise, a new distributor cap with contact screws
that actually do reach the centers of the wires eliminated the bucking and
snatching of the B. At first, I thought it had done nothing, because the
engine would barely run right after I installed the new cap and wires, but
apparently some of the plugs had gotten very fluffed because they had
been getting intermittant spark. They cleared within a half block, and I drove
it to work today. Still idles rough, but no problems on the overrun.
Feels and sounds good under power or at steady speeds. Thanks for all the
suggestions.
Question 1: On the trail of the cause of the rough idle, I tried to check
the timing last night, and there do not appear to be any timing marks on
the timing chain cover. The engine is a 69 (I said earlier it was a 68,
but the owner was wrong--it is an 18GH engine with a number under 8000).
One book shows a notched scale that projects out from the timing chain
cover toward the harmonic balancer. Where is it supposed to be? I
cleaned off the cover, and can find nothing attached to it or pressed into
it. Is it on the top? Which side? I cannot find *anything*. I put the
timing light on, could see the mark on the harmonic balancer (it was at
about 10 o clock as you face the front of the engine) but no sign of a
scale anywhere near.
Question 2: With the engine idling at an indicated 1200 rpm, revving the
engine does little to the position of the balancer timing mark. It is
hard to say what disconnecting or reconnecting the vacuum advance does to
the timing mark--not a lot, I think. I tried turning the vernier adjust,
and it was frozen. Does it sound as if the centrifugal and vacuum
advances are not free? Good grief! When I pull the vacuum line off the
vacuum advance, the engine speeds up noticably. I assume it is running
very rich, but if I try to lean out the carbs it runs worse.
Question 3: the books say to balance the carbs, then to adjust the jets
of the two carbs in the same direction simultaneously, one flat at a time,
seeking the fastest idle. But what if the mixtures of the two carbs were
radically off to start with? Say one was lean and the other rich. As you
make both richer, one gets righter and the other wronger, or vice versa.
What do you do then? Is the only approach to bring both jets up to the
bridge, lower each 12 flats, and start over?
Thanks for all the fish.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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