As I said, I'm not hands-on familiar with this particular carb model so
I couldn't have known a one "specific" cause. Was just giving you
general possibilities. However, that internal needle being adjusted too
lean very may well be the cause of your lean surge.
However, more likely though, Lawrie Alexander [Lawrie@britcars.com] has
already posted the answer for you and how to test/fix it. Your EGR
valve. Check out his post. Lawrie has proven to be one of the most
"reliable" tech sources on this list. See, I told you somebody would
probably know.
Valve adjustment won't cause a surge and the difference between .15 &
.14 is so minor, I wouldn't worry too much about it. We used to
sometimes run valve clearances a little looser that OEM recommendations
anyhow when I was racing. That little bit never hurt anything. However,
"lean burn" CAN damage valves and valve seats over time. You need to pay
attention.
-Jerry Erbesfield
73 B Black Beauty roadster
jerbesfield@mindspring.com
website- http://jerbesfield.home.mindspring.com
-----Original Message-----
From: MonteMorris [mailto:mmorris@nemr.net]
Sent: Sunday, August 25, 2002 9:32 PM
To: Jerry Erbesfield
Subject: Re: surging
Thanks for the detailed reply, Jerry. I'll check these things out. The
ZS carb has an internal, adjustable metering needle that I mentioned
that I had adjusted to the most lean condition. Maybe I just need to
richen the mix a little. Monte
----- Original Message -----
From: "Jerry Erbesfield" <jerbesfield@mindspring.com>
To: "'MonteMorris'" <mmorris@nemr.net>
Cc: "MG List" <mgs@autox.team.net>
Sent: Sunday, August 25, 2002 3:52 PM
Subject: RE: surging
> 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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