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MG MGB Technical - Shut Down....

Hi everyone, new boy here and I hope you can help. Last night my car died on me and I wonder if you could give me some advice.

It's a 1972 mgb roadster, pretty good nick, never really had mega issues with it before but recently I changed it from 2 6v batteries to 1 12v.

I drove approx 10 miles last night and while idling the car just shut down. No prewarning, it didn't cough and splutter, the engine simply shut off. I tried to restart but no joy. Plenty of charge in the battery. It was turning over well but did not fire. I called out my breakdown service who arrived and tested the spark. He disconnected one spark lead and the engine fired. We turned off and reconnected the lead and the car fired immediately and, as he said "sounded really sweet".

He could offer no solution other than "if you disconnect one it gives you a stronger spark to the other three which should get you home OK" but obviously this doesnt cure the underlying problem. Has anyone any ideas as to what the problem could be? The car is pretty much stock, no electronic ignition (yet) so your invaluable help would be very much appreciated.

Ric
Ricardo Vincenzi

The 3 is stronger than 4 is not correct. Try changing you capacitor, they can fail with heat and recover as the under bonnet temp goes down. Another possible is an LT side poor connection and while working under the bonnet it was disturbed and made contact again.
S Best

Thanks S, for your rapid response. Sorry, I'm a total novice. Can you tell me what you mean by "LT side poor connection"? What components should I be looking at?

Thanks again
Ricardo Vincenzi

I agree, and in fact I've had the exact same thing happen to me (faulty LT crimp). The LT connections are the small wires which connect to the coil - the coil being the cylindrical thing with a big fat wire connected to the middle which goes to the distributor cap. Check the connectors are sound.

Tim.
Tim Jenner

What nonsense, and from a breakdown service to boot. I just wonder if the fuel pump stopped and the car idled until the carbs ran dry. Fiddling around, switching on and off may have started it up again and all seemed well. It's worth a check and cleaning the pump points.
Iain MacKintosh

Thansk guys, and thanks Tim. You found my level of expertise!

The car did overheat and the Kenlowe kicked in so things are much clearer now. Thank you so much
Ricardo Vincenzi

This is probably a silly question that may be difficult to answer but would electronic ignition solve this kind of problem?
Ricardo Vincenzi

Not if it's just a loose LT connection - in fact, my problem was cause by me not crimping the connector properly when I fitted electronic ignition!!

Tim.
Tim Jenner

Hi Ricardo, welcome.

Electronic ignition does reduce the maintainence needed, but I wouldn't guarantee that it will solve your prob.

MGB's are generally easy to work on, I suggest you scour the second hand book shops, car boot sales and charity shops for a copy of 'AA BOOK OF THE CAR' (Published around 1970, has a silver / grey cover) which gives a really clear insight into the way cars of the MGB's era work, and how to maintain them.
I also recommend 'Be your own car mechanic' by Chris Webb, also published in the 1970's.

Don
Don

Ricardo

If not already obvious, LT = Low Tension i.e. the 12v circuit wiring as compared to the HT or High Tension wires (from coil to cap to plugs).

I have a pertronix ignition module in the distributor which essentially replaces the points and capacitor - it has given me 3 years and 10,000 miles of trouble free service to date. As Don mentioned it can reduce the maintenance aspect of keeping the points correctly adjusted however some people warn that electronic components can fail suddenly and without warning. If a points replacement device, such as the Pertronix is installed, it is recommended that the removed components be bagged and kept in the glove compartment TOGETHER with the required tools.

Good luck and welcome to MGdom.

Barry
73B
B.J. Quartermaine

Hi, Ricardo - actually, for a novice, conventional ignition may be better, as BJ notes above. Easier to understand, as there's only one "electronic" part (the condenser, or capacitor), and the rest is mostly mechanical. Purists might say the coil and switch (points) are electronic, too, but they're just nit-picking <grin>.

You might also want to look at the point gap carefully, as one which is only barely opening can produce the symptoms you note. In fact, as the point rubbing block wears, it is possible to have fire on only a portion of the cylinders, as the distributor cam is often slightly asymmetrical. A light smear of grease on the cam is crucial to keeping wear to a minimum, but don't 'glob' it on, or the grease can foul the points quickly.

Hope you get many "miles of smiles" - - Alec
Alec Darnall

The sort of problem experienced could be caused by many things. One post noted the fuel pump and that's a good point. I gather the MGB is new to you and you'll need to acquaint yourself with the muffled chatter of the electric fuel pump when the ignition comes on. The 72 ran twin SUs and you can start and drive for a ways with the fuel already held in the carburetor fuel bowls. Not sure about 10 miles though. Your tire kit should have a soft head hammer in it. I've used it more than once in earlier days on a 1970 B to tap the fuel pump just inside the rear passenger tire to get it going again. Do it lightly though. I noted that Moss now has an electronic SU fuel pump, but cleaning your points is a lot cheaper. You did mention changing the battery and I would make a suggestion that you check the cables to the battery. It's a long shot, but my '80 LE would occassionally stumble in a turn like the key got turned off and I found the ground cable to the battery was loose and replacing it cured it. By the way, those twin 6 volts served a very good purpose in cold weather. They delivered more cranking amps than a single 12 volt. If it's a '72, it's likely a high compression engine. The plate on the passenger side of the block just below the cylinder head will end in "-H" if it is. You should be OK in England though.
Rick Penland

This thread was discussed between 17/08/2005 and 18/08/2005

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