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MG MGB Technical - Sometimes car doesn't start after use....?

Hi all,
I've had this problem for a while and have been too lazy to investigate or do anything about it. I'll start my car up and it'll run just fine (well, that's relative) around town to the store, or where ever. But, I'll shut it off, do my errands, and I'll get back and the car won't start!!! No power!!! I'll click once and then just die. It'll stay in this dead state for 15 or so minutes after which, if I try to start it, it'll fire up fine. It's like something has to cool down. It's got a new Bosch alternator and a battery with good charge. My friend who has a rubber bumper B said that it might be the ignition coil. What do you all think? My car is a 1973 B, stock. Thanks so much!!!

Alex
Alex

Alex, When you have the no start problem does the starter turn the engine over? What do you mean by "no power"? Clifton
Clifton Gordon

Alex-
The 1973 model has model AUD 550 SU HIF4 carburetors. These have a thermosensitive mixture adjuster compensator in the form of a bimetal strip. If the insulation on your heatshield is shot, then the heat from the exhaust manifold gets through and the mixture adjustment goes so lean that the car won't start. In addition, the heat from the exhaust manifold percolates away the fuel in the float chambers, requiring you to wait until the fuel pump refills the float chambers. When the bimetal strips in the carburetors cool, the mixture is back where it should be and the car will start (see how easy that was to understand?) Check the insulation on your heatshield.
Steve S.

It is not a fuel problem because he says that the car clicks once and then nothing. If it was a fuel problem then the car would spin fine but would not catch. It is an electrical problem. I would check the system from battery connection forward but I suspect is it in the engine compt. I would search some of the online help sites for trouble shooting if you do not get a definitive answer here.
My $.02 worth
Carl W French

Hi, sorry for the misunderstanding. Carl is right. When this happens (and it doesn't happen all he time), it clicks, and there's no power ANYWHERE. The stereo doesn't work, the interior light doesn't come on. How odd.

Alex
Alex

Alex,
Sounds like it happens on a thermal cycle, and since there's little or no power, I'd suspect something closely related to the battery. Either something internal to the battery itself, or the terminals. Heat cycling can cause damaged battery plates to move around, and can affect the resistance between the cables and terminals. Less likely at the earthing point. Just a thought.

Best, Joe
Joe Ullman

Alex, Thanks for the additional information. Adding to Joe's suggestions, if your battery cable terminals on the battery end have the local $1.49 bolt on terminals I would suggest carefully checking for corrosion between the terminal clamps and the cable. Good luck, Clifton
Clifton Gordon

I've always had the experience that cold and wet weather case battery and terminal problems. I've never had heat be the issue, although I'm far from being an expert.

What Clifton says is definitely the first plan. I'd clean and tighten the connections between the clamps and the battery and the clamps and cables if they're those bolt-on jobs. I'd clean and tighten where the battery ground cable meets the car, too.

I'd also clean the connections on the big wires at the starter, and check for loose terminals both on the cable and the starter itself. Check the connections on the alternator. Clean if neccessary.

An interesting test would be - when the car refuses to electrify, put a test light on the bottom terminal of the starter. This is the main connection to the battery. Any voltage? If not, that isolates the problem to the battery, cables and ground strap.

You said the interior light doesn't even come on. If you find you were mistaken, then you may want to check your wiring to the ignition switch. I've had brittle wires break at the connector plug to the ignition switch. But this would not affect your interior light or headlights.

Please let us know what you find to be the solution. These is an interesting problem.
Matt Kulka

Thanks everyone for the great suggestions. I will bookmark this thread and add to it as I find time to tinker with the car. May not be for a while though, it's cold out, and my garage is barely large enough for two cars.

Alex
Alex

Alex, many years ago I had a similar problem with my first MG. The heater hose had a pin hole leak and would slowly drip into the distributor just below it. It would run fine for a while and then refuse to start until the moisture evaporated from the distributor. Not knowing enough in those days to check the distributor for moisture, when the hose finally burst and I replaced it, the problem was solved.
Bob Hacker

About the ignition coil (I bought a new one just in case), what happens when it starts to, or goes, bad? Are there any symptoms? Fouling of plugs? Weak sparks? Missed sparks? Thanks.

Alex
Alex

This thread was discussed between 06/02/2003 and 08/02/2003

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