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Technical Area => Upkeep and Performance Hints => Topic started by: june2017 on May 03, 2017, 11:03:48 AM

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Title: Spark plug carbon fouling
Post by: june2017 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
Title: Re: Spark plug carbon fouling
Post by: JohnTwist 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

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