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MG MGA - odd engine problem

Hi everyone,

I have a strange engine problem. It seems that half of my pistons aren't firing. Nothing strange there, but here's the situation:

I have a cross-flow head so the gas flows to pistons 3 and 4 first. When I pull the spark plugs for those pistons, the engine sounds the same. But I have a spark going to those pistons and when I pulled them out, attached the plugs and fired it up, they were sparking. (The engine was so loud and vibrating so much, however, that I can't say for 100% certain that it was sparking at the gap. I looked like it, though.)

The spark plugs were blackened. I figured this was because the mixture was too rich as I was waiting to have someone help me adjust the carbs and all of my plugs were blackened. The exhaust is a little black.

Both carbs (SU) are drawing air in. I put my hand over the front carbs (cylinders 1 and 2) and the engine stalled and my hand smelled like gas. I did the same thing on the other carburettor and the engine stalled but my hand didn't smell like gas. Is it possible that the carburettor for cylinders 3 and 4 isn't giving those cylinders gas? I currently have both carburettors at 1.5 turns from fully closed.

Sorry if this is a stupid question, but I really don't know what's going on here. I took my car for it's first drive since it was apart and the engine sounded bad, but I thought was just the timing. I loved driving it, but it was sluggish after 3000 RPMs. Called someone up and he pointed out that from the sound of it not all of my pistons were firing...

Any ideas would be welcome.

Thanks,

Darian
Darian Henderson

I wish not to be offensive but this is simply a set up situation and by the sounds you don't have the knowledge or ability. Let you buddy get there and everything will be fine for sure.
Assister

Your pulling the plug wires and there not being any difference in speed points to those 2 cyls not doing any work. Focus on that carb.

Sounds like you have done quite a bit of analyzing, time to dig a bit deeper. You're on the right track, seems to me. It's so fulfilling to fix it yourself, sometimes the lightbulb comes on and you go "DUH", why didn't I think of that earlier? Somebody might be able to find the problem faster, but finding faults is all pretty logical most times.

Maybe this exact problem has happened to someone here and they can help more than I can. Your timing light can be hooked to any of the plug wires to see if there's a regular spark. Is there crap in the float bowl?
Tom

Darian
Read the manual on how to set up the carbs, and follow each step to the letter. It makes no difference to carb setup that you have a different head.

I recall that you recently had an issue with timing, so if you have that set correctly, and the engine was running OK, then you MUST set the carbs together to get the engine running correctly again. Once they are set, leave them alone. Apart froom topping up the damper oil, they can be more or less forgotten.

Dominic

dominic clancy

#3 and #4 plug wires switch? Take another look at the distributor cap. Firing order is 1-3-4-2. with rotor turning anti-clockwise. Otherwise, not the right fuel mixture on the rear carb, possibly running very rich, maybe flooding.
Barney Gaylord

Were the spark plugs blacked with soot or oil? Perhaps some plugs are severely fouled. After checking the other things that have been suggested, consider measuring the compression and trying another set of spark plugs.
Steve K

Hi everyone,

Plugs 3 and 4 were in the right place. The spark plugs were covered in soot. I think I have to take Dominic's advice and look at the carbs better.

Thanks,

Darian

Darian Henderson

How fresh is the gasoline? If it's been in the tank for year, I recommend replacing it before attempting to tune the carbs.
Steve K

This thread was discussed between 19/08/2007 and 21/08/2007

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