I don't know the specifics on your exact model carb but maybe I can help
anyhow. I'll give it a try. Here goes:
In general, on ANY automobile, real surging is almost always caused by
the engine receiving too lean of a fuel mixture (too much air/too little
fuel) from the fuel system, and I'm not talking about adjusting the
external adjusting screws leaner or richer. In gasoline powered
vehicles, on most conventional carbs, the external adjustments control
only idle speed and idle mixture, NOT the running at speed mixture. At
speed, on most conventional carbs, internal hardware controls
richness/leanness. Items such as jets, needles and seats, power pistons
and such. In the 70's, with the fuel shortages that were being
experienced in those days, it was a big thing for the auto manufacturers
to produce engines that ran as lean as possible, to get max emissions
reductions and fuel economy. Because those 70's/80's engines run so lean
anyhow, it oftentimes doesn't take much to upset the delicate balance
and make an engine surge.
If it were my car, here's how I would go about correcting "lean surge":
1). The first thing I'd look at was the fuel supply, such as the fuel
filter to see that it is not stopped up.
2). Next, make sure that the fuel line is not restricted, crimped, bent,
partially stopped up or something like that.
3). Make sure that you are getting gas to the engine, not something else
such as water sugar, dirt, etc.
4). Make sure that your point gap and dwell are correct. I have seen
this "contribute" and magnify a pre-existing lean surge that was not so
noticeable previously.
5). From your comments, I assume that your engine is otherwise in good
shape. No intake manifold vacuum leaks, tuned decent, clean/unrestricted
air intake filter and such.
6). If all of the above verify as correct and functional as per design,
and you haven't overlooked any of the obvious, then, unless this
particular model has something weirdo in the emissions system or
elsewhere that could cause it, which IS possible, (other list members
should let you know real quick!) then something internal in the carb has
either stuck or become gunked up or blocked. You'll need to disassemble,
clean, replace gaskets and seals and unstick anything that might be
stuck.
If it didn't surge previously, after the above work is done (properly),
it shouldn't surge any more.
Good luck!
-Jerry Erbesfield
73 B Black Beauty roadster
jerbesfield@mindspring.com
website- http://jerbesfield.home.mindspring.com
-----Original Message-----
From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net] On
Behalf Of MonteMorris
Sent: Sunday, August 25, 2002 3:03 PM
To: MG list
Subject: surging
It's a beautiful afternoon here in Missouri and we are going for a
cruise in the 67.
Our 79B with ZS carb seems like it is "surging" a little while driving.
Not very noticably, but I'm pretty sure it is. The carb has been
adjusted to as lean as it will go and the car seems to run fine-will do
at least 80mph (more if I'd let it) and doesn't ping or cut out. I set
the valve clearance last January and set it wrong (at .015) and have
been driving it since April this way. I just reset it to .014 hot, but
it has seemed to surge for a long time. Any ideas?
Monte Morris, Kahoka, MO
79B, Carmine
67B, BRG with dreamy suspension
74 1/2 parts car
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