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MG MGB Technical - '77 MGB won't start

My '77 MGB started backfiring slightly when I would let off the gas. Then suddenly it just quit and wouldn't start. Towed it home where it sat for several weeks before I could look at it again. I pulled the carburetor (ZS) off, took it apart and cleaned it (has been rebuilt fairly recently) and everything looks good there. Checked the fuel pump, you can hear it cut on and also pulled the line off the carb to verify fuel was getting in there. Fuel is clean, no trash and no water in it. No apparent vacuum lines missing/cracked (the emissions control equipment has all been removed by a previous owner).

Replaced the coil, even though the old one appeared to be OK, and checked for power to it. It's OK, and the distributor is sparking, but no fire is getting to the plugs. Put the tester on the (fairly new) distributor cap lead (to the plugs) and no juice there either. The plug wires are in the correct position.

We had checked the timing at the time the carburetor was rebuilt and it was fine then. I'm stumped as to what the problem could be, and what would bring it on so suddenly. Other than the slight backfiring, the car was running fine up until the point it cut out.


C Black

Check high tension, (secondary)wire from coil to distributor.

Look for good clean connection and condition of wire --- too, that it's not grounding out on something like the oil dip stick.

Also all the stuff with the rotar.

Take two aspirin and post results in the morning<;+}
glg

Sounds like a bad rotor; sometimes they get a crack and ground to the distributor shaft. A bad distributor cap can also do this - a crack or crud buildup inside gives an alternate path for the spark.

Tom G

Maybe your timing is off now. Check the locking plate, it may have come loose allowing the distributor to vibrate out of place. I don't suppose your Opus ignition is still intact so you might also check that the trigger mount of whatever replacement you have is in position.

Doug
D. Cook

Check that your points lock nut isn't loose and the points stuck closed...not that this has ever happened to me <wink, wink>.

erik.
erik

Two coils bad? Hmmm. If you say you have no spark pull the coil wire out of the coil a little way while someone cranks (you won't get a shock holding that end). You should be able to hear and see (might need a mirror) the spark. If so but none at the plugs then either or both of the rotor and cap are bad, change both, or all four (!) plugs are breaking down. If no spark at the coil then either the second coil *is* bad or somthing else is wrong with the LT circuit. Again while cranking measure the voltage on the coil +ve and -ve. You should see about 10v on the +ve and switching between 0v and 10v on the -ve. Use an analogue meter if you can, a digital may not 'settle'.
Paul Hunt

This thread was discussed between 24/10/2003 and 25/10/2003

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