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'77 MGB with Carb Problems - HELP

To: MGS <>
Subject: '77 MGB with Carb Problems - HELP
From: Rich Peterson <>
Date: Sat, 01 May 1999 23:27:19 -0400
My '77 B appears to have developed carb problems and I can't figure out
what is wrong.  Background:  The car has 110,000 miles, good compression
(130 +/- on all four), luminition electronic ignition, desmogged engine,
original ZS carb which was rebuilt a few years ago, manual choke
conversion, new plug wires, new NGK plugs, timing set to 15 BTDC w/o
vacuum advance and it runs on 92+ octane gas.

The problems I've developed are:  Bad misfire while warming up from
cold; poor fuel economy (20 MPG); excessively rich mixture (black, sooty
plugs); poor hot restart; idle falls to about 400 rpm when hot (fans

I've tried to lean out the mixture, but the needle is all the way down
and it is still running rich.  I've lowered the float level, but that
doesn't seem to make any difference until I hit a certain point - then
the car won't run.  I get about 18-20 inches of vacuum at idle, so I
don't think I have a vacuum leak.  I've readjusted the manual choke
conversion, so I don't think that it's the problem, although it's the
most suspect at this point (i've tried swapping the choke body with
another that I have with no change in the problems).

Once the car reaches operating temperature, it seems to run well,
although there is an irregular miss at idle.  It has good power and
pulls well throughout the RPM range - I feel a definite surge as the RPM
moves past 3000-3500 rpm under full throttle acceleration and it feels
especially strong between 3000 and redline (gotta have some fun to ease
the pain of my problem . . .he he).

Any guesses?  It has me baffled.  I'd love to replace the ZS with a pair
of SUs, but the budget (SO) won't allow it, so I must fix this problem
with existing hardware.


Rich P.

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