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MG MGB Technical - Questions

Hi all, Im new to this MG thing, I bought a 1980 MGB. It idles very rough, I changed plugs yesterday, they were black. Went to do a compression test today, plugs were again black. Compression from #1, 135, 115, 140, 145. Is the problem the low cylinder, or the carb.? It has a single Carb., I believe a Zenith. Where is the mixture adj.? Thanks.
Tom D

Tom

Sound like you're running rich. First things first though, get a Haynes or Chilton's or some other manual for your car.

Then, always check your ignition system thoroughly before even looking at the carb. Set the timing, check the vacuum advance. You should be able to suck on vacuum tube to cause the points plate to move. It shouldn't leak down.

Next start looking into the carb for problems. Make sure the choke isn't stuck. Be careful with the ring that holds the choke housing in place its easy to strip the 3 screws.

Don't try to test drive the car without the air filter installed. I had a zenith that just wouldn't run worth a sh*t unless the filter was in place.

The mixture is adjusted by removing the dashpot cover and using a special tool that holds the damper while the mixture needle is turned. You can hold the damper with your fingers ( to prevent it from turning and thus tearing the rubber that mounts it) while you turn the mixture needle with a hex wrench.

I wouldn't worry too much about the low cylinder. If you want, you can put a teaspoon or so of oil into the cylinder. If the pressure comes up, the rings are at fault, else look at either unseated valves or a head gasket leak.


Mike
Mike Phillips

This thread was discussed on 18/11/2002

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