MG Midget Forum

My 1974 mkIII Midget is running very poorly. The engine seems to hesitate, and I think something is wrong with it besides being timed not very well. I attached a picture of the spark plugs after I removed and cleaned them, then put them back in and ran the car for a couple minutes. Recently it has been run with 20% too much oil, so I think that my have something to do with it, but it now has the proper amount in it. The middle 2 are very slightly oily, and the other 2 are black because we have to run the car with full choke, otherwise it dies. The flexible hose lines are slightly kinked, but that will be fixed tomorrow. Thanks for any help or advice.

If youre in chicago you can't be far. I'd love to help in person. PM sent.

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Seth Jones

1971 MG Midget

www.SpridgetGuru.com

Atta boy Seth!

Looks like he has some tuning up to do!
Nice of you to offer to help! That's the great thing about this website and group of individuals.

Ice

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Iceman

Atlanta GA

71 MG Midget

62 AH MKII
67 Midget
71 Midget

I hope you let Seth help you. Don't mess with those plugs, replace them bu the cause of them being like that needs to be fixed first.

Seriously.

here's suggestion on setting mixture

First, (assuming you have valves adjusted right and timing right--if these are off, you won't be able to properly set SUs as the vacuum will be off and SU relies on vacuum) make sure the linkage is properly set up (throttle shaft clamps properly set, fast idle correctly set, etc)

Make sure float level is correct. Float level will directly affect mixture. Position jet 70 thou down from the bridge. This is a starting point, not final setting. Eyeball throttle clamps so each carb starts opening at same time. If adjustment is needed, remember that if clamps are tight, tweaking one will tweak the other as well, carrying on the maladjustment.

Start car and get engine warm. Drive down the street at 15mph in as tall a gear as you can get it to run in, probably 3rd. Very, very slowly accelerate to about 25 mph, not changing gears. If it stutters, richen each carb a little, by the same amount. If it does not, lean each carb by the same amount and re-test. When it is stuttering and the richen phase solves this stutter, then go to a faster road and repeat at less than 2000 rpm in as tall a gear as you can. Probably around 30 in 4th. Slowly accelerate to about 45. If it stutters, richen both carbs a little.

When that's done, synch the carbs with your favorite tool. Set idle at about 750-850 rpm (it will fluctuate if there's wear in the distributor, points are worn, or timing's off). Repeat the initial mixture test. It should pull smoothly at very slow acceleration. If it stutters at high acceleration, increase the viscosity of the damping oil in the dashpots.

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1973 Pale Primrose Roadster. A nice 10-footer!
SUs, Datsun 5-speed

I have taken Seth Jones up, and he came out today and helped look at everything. He located a lot of things that might be contributing to my problem, and as soon as some parts come in, I am sure that it will run beautifully with his help. Thanks again, Seth.

You're welcome!

BTW for those who weren't there. . .

I ran a compression test and all cylinders were between 145 and 152 psi so thats good. Points gap needed some adjustment (too wide), valve clearance was a tad off. One carb was missing an idle screw. Plug gap was also a bit too wide on all plugs so I adjusted them all to .026". Throttle shafts were worn but one was worse. The carb with the worse shaft also had the throttle butterfly off center such that there was a considerable gap around the top of it when it was "closed". Fuel pump is new. Recommended new throttle shafts and butterflys as the ones in the car were they kind with popoff valves which I have heard are not trustworthy. Car has a Bosch Blue coil of the type that Jeff at Advanced Distributors sells.

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Seth Jones

1971 MG Midget

www.SpridgetGuru.com



Edited 1 time(s). Last edit at 2014-08-21 06:36 PM by AmishIndy.