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MG MGA - Continuous misfire- HELP!

Guys,
My friend has a nicely restored 61 1600, engine was rebuilt when he bought it 20 years ago but NEVER started (long story)until last weekend with fresh fuel. The engine has a continuous misfire. When I pull plug wires, with the engine running, I observe a rather anemic yellow spark on each cylinder. No matter which spark plug wire is completely unhooked the engine seems to run the same. Checked the plugs, the front two are sooty (black) the rear two are sooty and somewhat wet. The carbs have been set to factory specs. There is no overflow from the vent tubes. Have changed all electrical components (cap, wires, condensor, coil, rotor)with known good ones and checked the voltage to the coil...no change. New points. Had the distributor on the bench, point gap is fine, distributor wiring is fine, mechanically seems OK.
HELP!

Gerry Foster
G T Foster

Gerry - is it really continuous, even at idle and no load? Never hurts to check the ground strap.

- Ken
Ken Doris

Are the carbs balanced correctly, with the correct needles - it sounds as if it is running too rich and the timing is way out. Is the correct crank pulley on there for the timing marks?

A few other checklist suggestions

Are the valves set properly ?
Is the rear air filter on upside down (beat Stevie G to that one this time!)
Is the vacuum advance connected and working?


dominic clancy

What you describe sounds horrid. Have you checked that all the valves are closing? That is none are stuck open. If the engine hasn't got really hot you probably will get black plugs, especially with the choke out. Have you checked the choke adjustment screw is correct and the jets are fully returning back up to the nut.
Any more clues as to what you have found here???
Pete
P N Tipping

Guys,
It turns out that the distributor drive was installed out of position (maybe one or two teeth (Engine done 20 years ago). Once corrected the engine runs sweet. Thank you for your input. I love this Web site. You guys are the best.
Cheers.
Gerry
G T Foster

Gee thanks Gerry! Well done finding that mate.
Pete
P N Tipping

Surely it shouldn't make any difference where the distributor drive is engaged, providing the spark is correctly timed and the plug leads connected to the appropriate plugs?
Lindsay Sampford

I don't think one could "correctly time" the distributor if the drive is one or two teeth out of position due to the timing relation to the valve position. Or, it would be an unnecessary PITA to do so!
G Goeppner

So I was right about the timing being out, but this could easily have been checked with a timing light before going round the houses...
dominic clancy

It is possible to get the timing spot-on with the distributor drive out by a tooth or two by twisting the distributor round to compensate, and/or wiring the plug leads to the cap in a 'non-standard' way to get the spark to the right plug. I have come accross this more than once, usually when fitting a new cap and leads wired the right way! http://mgaguru.com/mgtech/ignition/ig103.htm
Lindsay Sampford

Hi Lindsay
Well you certainly can do that and I too have had occassion to see this. However you do tend to get the vac advance inot positions where the rigid pipe will struggle to fit and other times when the vac unit fouls the block.
I do think though that many people do not time the car correctly and simply assemble the distributor in the way it is shown in the manual and do not therefore double chech where the spark is directed

I am surprised it actually started. One would think that if it started it would run OK but have no power?
Robert (Bob) Midget Turbo

I understand that it is possible to crank the distributor around, however, the owner assured me that he had "statically" timed it and it was spot on. It was a pretty easy thing to fix once found.
Cheers,
Gerry
G T Foster

Gerry, I think that the key thing you did, apart from putting the distributor drive right, was to time it correctly!
Lindsay Sampford

Well that is correct Gerry you can statically time the car on any plug doesn't mean that the sparks are going to the correct plug which appears to have been the problem. :)
Robert (Bob) Midget Turbo

Just goes to show that regardless of what people say, it's always better to start from the beginning and rule nothing out
dominic clancy


G T, You said in your initial post. " I observe a rather anemic yellow spark on each cylinder. "

Seems to me if you had an anemic yellow spark that condition would still be there. Did you in all your checking around the engine change the point gap or other item to get a good blue snap across the gap? Or is the spark still poor?

Ray
Ray Ammeter

Ray,
Truthfully, we were so happy (and tired) when the engine ran the spark was not re-checked. But I have been thinking about this an will do so this weekend.
It's also important to point out that another, fairly young, member of our club provided valuable trouble shooting assistance.
GTF
G T Foster

This thread was discussed between 11/04/2011 and 14/04/2011

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