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MG MGB Technical - MGB ignition failure

any ideas ?

car ran beautifully... stopped in car park and couldn't restart engine - had to be towed home.. now with car in garage - new points and coil.. same problem.. starter motor ok, spark yes, ignition NO.. fuel pumping.. twin carbs - both failed? what could fail so completely with no warning - that I am not thinking of - or what is now wrong that has the same result.. electrics seem ok but the engine doesnt fire ?
swilson

I don't understand; spark yes, ignition NO. Do you have spark at the coil? If yes, do you have spark it the plugs? If no, you probably have problems with the cap or rotor going to ground.
Leland Bradley

Hi

Runs well but won't restart after a brief stop is a common symptom of vapour lock.

If you are getting a good spark at the plugs, try turning the engine over and then removing a plug, the plug should be a little damp and should have a strong petrol smell.

Don
Don

Yeah, what's that mean spark yes, spark at all the plugs? What color spark?

For fun, check the distributor cap -- the carbon rod that takes HV charge from the rotor -- check the condition of the rotor and distrib contacts.

You did not mention a new condenser.

From what you describe, my guess is a not-up-to-par spark.

Of course that's just my opinion. I could be wrong.


glg
glg gimbut

I want to replace my ignition switch but the new one does not fit in the 1968 MGB place for it. What's weird is that the old one that just came out doesn't fit back in either. Am I losing my mine? How do I make either of them fit? Thanks.
gkiser

If you have a later car, it's well worth checking the ignition circuit relay under the bonnet (mounted in front of the fusebox, on the inner wing). If it starts to fail, it can give some very odd symptoms.

Good luck
Bruce
B. Mann

Vapour lock is almost impossible unless the carbs get so hot that the fuel in the jet vapourises - very unlikely especially in the UK im April, particularly after being towed home and then it won't start in the garage. If you have fuel in the jets (blow in the overflow pipe and see if it comes out of the jets) and spark that really only leaves the possibility that the spark is occuring at the wrong time i.e. the distributor has slipped? Mind you, where do you have the spark? Unless you can clip a powered (12v) timing light on to each plug lead and see a flash when cranking you don't have a spark at the plugs.
Paul Hunt

You can have spark at the HT lead to the distrubutor, but no spark to the plugs. A bad dist cap or rotor can cause this problem.
Rob
R. L Carleen

I fitted some little terry clips to an aluminium sheet, put the plugs in the clips, connected the HT leads to the plugs and an earth lead to the plate.

Next I turned out the lights and watched the sparks run along the plugs when i cranked the engine. By the way, this can give a useful check of firing order - more important on a V8 than an S4!

good luck

peter
P L Hills

This thread was discussed between 09/04/2003 and 14/04/2003

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