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MG MGA - Will not run right

Help, I have just endured fuel pump hell and now something else is going on. After, I hope, the fuel pump problems have been overcome I find that the engine will nor run smoothly. Could it be a problem with the fuel pump still? I do not know. When I start the engine it barely runs. I remove spark plug wire #4, the rear on, and it runs much more smoothly. This should not be but is. I do not understand. Why should something go wrong just as soon as something is fixed? I have cleaned the bowls and checked the flow and all seems good. I did the air in the line check and alls good there. Just two days ago is ran like a new one. Oh, it seems that the spark to the rear two cylinders is stronger than the front two but the rear plug when the wire is replaced shuts the engine down. It also starts much better with the rear plug disconnected. Could it be the points, the dist is all of a sudden worn out? The plug wires are not crossed but may need replacement. Help, Neal Turner
Neal Turner

Neal. Dave Dubois lists fuel pump pressure and volume specifications, as well as an article on trouble shooting the fuel system at www.custompistols.com/ on the MG section. That should handle most of your fuel related questions.

However, it sounds to me like you have your spark plug wires in the wrong order. Firing order is 1-3-4-2 and is in a counter-clockwise order when viewing the top of the distributor cap. The only way an engine will run better when you disconnect a spark plug is if the spark plug is firing at the wrong time. Then the engine is fighting the fired cylinder as the piston is being forced upwards against the expanding gasses or it is being fired on the exhaust stroke of the cylinder.

In any event, the website I referenced also has some information on ignition system trouble shooting and basic engine timing which may be of use to you.

Les
Les Bengtson

Les, I just tried switching the plug wires and got a huge POP and nothing else. I believe that you are right about one plug fighting the other but there must be some other explanation. I was thinking a bad dist or perhaps points out of order. It is hard to believe that it runs fairly good with the offending plug wire off. I recently had a reworked MGA head installed and it ran fine untill the fuel pump quit and now, assuming that the fuel pump is not the culprit. Alas, the weather is great to go for a long drive. Thanks, Neal Turner
Neal Turner

If the wires are on properly (verify first) removing a wire from a funtioning plug should normally cause it to run worse and slow down. If there is a crack, or carbon, track between two terninals in the cap the spark will go to the wrong plug of the pair because there is more resistance in the plug that should be firing. If that is the case then removing one of the two wires will cause the spark to go to the remaining plug twice. That is probably why the engine runs better with three wires on than four. Check the cap it is likely bad. I alwasy replace cap rotor and wires as a set.
R J Brown

I had a similar problem with my Austin Westminster. It would run ruff with all 6 cylinders and when I pulled No.5 it ran smoothly. The answer was a small crack in the distributor where number 5 lead exists the cap. I would change the cap in case you have a crack you can't see, as per above.
Cecil Kimber

Well you hit it on the head, Stinkin cracked cap just where the wire exited to go to the rear cylinder. The crack also extended to the coil wire exit. I hope that this is the problem. I have two new caps and rotor buttons on order from Advance auto. Thanks, Neal Turner
Neal Turner

The lads quite rightly suggested a cracked cap but they were actually suggesting a micro crack that would have been almost impossible to see with the naked eye. If you can see a crack then if it is not causing the problem it will certainly cause a huge problem shortly.
Bob (robert) Used to have 2 cats

How many cats do you have now Bob?
Art

Hi Neal. Remember: Lucas distributor caps aren't all they're cracked up to be!!!!! lol Glenn
Glenn

Hello, It was the cracked cap. It runs like a dream. Not a nightmare. Thanks for all your help. Neal Turner
Neal Turner

This thread was discussed between 01/10/2005 and 05/10/2005

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