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Author Topic: Spark plug carbon fouling  (Read 3517 times)

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Spark plug carbon fouling
« on: May 03, 2017, 11:03:48 AM »
I have a recent new to me 79 MGB and an having some serious carbon fouling of the plugs.
I'm looking for what might be the problem and can't find a straight answer for the following.
What would be an acceptable compression test reading? Also Correct firing order? This car will start and run when cold, I see it walk back on the choke cam as it warms. Once at operating temp it will not idle.
Any suggestions would be greatly appreciated.
California Car, with ZS 175 carb
Eric Beck


  • AMGBA Club Tech Staff
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  • Posts: 173
    • University Motors
Re: Spark plug carbon fouling
« Reply #1 on: May 03, 2017, 11:26:56 AM »
Your 1979 MGB was supplied with a Stromberg carburetor which has an automatic choke.  If this is still the carburetion on the engine, chances are there is a problem with the choke – or – more easily, there is a hole in the rubber diaphragm around the air piston in the carb.  
The compression should be, first of all, consistent within ten percent.  Figures from about 110 to 180 are OK – as long as they’re all within 10%.  The number three cylinder (third from the front) is always the problem cylinder.
The firing order is 1-3-4-2 anti-clockwise (counterclockwise).   Conventionally, the number one spark plug wire exits the distributor cap at 1:00 – 2:00.
Hope this little bit helps!
I do have some videos on YouTube that might be of some assistance you to.  Find them by searching for <universitymotorsltd>
John Twist
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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