Well, it seems as if I chose my words pretty well, albeit not perfectly,
when I referred to the bucking MGB. Only off by one letter. Reminder:
72 B with 68 engine, runs well under load, but bucks and snatches as it
decelerates. Lumpy, uneven idle, threatens to quit.
I called John Twist, who suggested the engine moving under deceleration
might interrupt the ignition. Indeed the coil to distr. high tension wire
looked a bit short. I measured infinite resistance between the cap center
button and the coil tower plug (stranded copper high tension wires).
Eureka, says I, a broken wire, intermittant contact, Twist's a genius.
He may be, but the wire wasn't broken. The el cheapo distributor cap has
aluminum terminals, with pointed screws that thread into holes in the
contacts from inside the cap. You cut the wires off square, push each
into the proper hole, and the point of the screw is then supposed to bore
through the insulation into the center of the wire in search of possible
contact with conductors. But the holes in the aluminum contacts were not
threaded to the bottom of the center and two of the side contacts, so
those screws became impossibly tight long before the point of the screw
punctured the insulation. There was infinite resistance not only on the
center terminal but on the contacts to plug wires 1 and 3. The pointed
ends of the screws were eroded by the sparks jumping to them. The miracle
is that the car would run at all, much less run well under load and not on
the overrun.
I have a funny feeling this is A problem, perhaps the cause of the bad
idle, but not THE problem. Anyway, the owner (who is a good friend) gets
a new distributor cap and wires out of the deal if I don't buy the car,
because I am *way* too anal compulsive to put this piece 'o crap back in.
That should be a carguy question--did you ever fix somebody else's car at
your own expense because you couldn't stand to leave it the way it was?
Thanks to everyone who has replied so far. If, as I expect, this is not
the problem or only part of it, I will work my way through the several
excellent suggestions. By the way, the car has HS4 carbs, vintage 69
according to the tags, for those who wondered. They have spring loaded
needles, apparently, whatever that means. But the lumpy idle is not very
responsive to minor tweaking of the mixture, so tentatively I doubt the
carbs are the major prob. Anyway, with this other junk wrong adjusting
the carbs would be pretty pointless.
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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