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MG MGB Technical - 77' MGB start and stall problem

one month with my 77' MGB has found some intresting problems, the car will start then stall after warm and than I can't restart the engin agin untill cooler.
glori

Glori: I don't have a 77, but years ago (i.e 1978) my best friend had a brand new one, and it did the same thing. He foreswore MGs forever, and the poor sot had to settle for BMWs instead...
I have heard that the Lucas electronic iginition system used then was notorious for that type of intermitent failure. Does your car still have the original distributor?
Andrew Blackley

Is the heat shield in place between the
catalytic converter and carburetor, and is
it in good shape? Fuel vaporization is a possible
cause of this.

Could also be an autochoke/carb problem -- assuming
you have the Zenith check the archives for
autochoke threads to start with.
Ronald

thanks for the prob solving, the distrubetor is orgional, and looks wondreful, car has 43,000 miles and lots of storage time, I will look into that first. the heat shield is in place and to me its marginal in the way it looks,and it is a zenith carb. i will look up in the archives for this now. I would love to get it fixed with out the shop but who knows?
glori

Glori,

Have 79 and 80 MGB. Dealt with same issues.

Essentially, the fuel pump was worn and when the car was driving around the fuel pump was not pumpimg enough gas to the engine. When the car cooled off I suppose the pump did too.

First replace the fuel filter, if dirty it will slow done delivery of the fuel.
Second, replace the fuel hoses (carb to filter, filter to fuel pipe, fuel pipe to pump, pump to fuel tank).

Third rebuild the fuel pump. I used the fuel pump rebuild kit from victoria british, Its a dirty job (under the car)but it can be done with simple tools & limited expertise.

John Long
John Long

Glori,

I suffered from the same problem in my '77B and went the normal routes described above (replaced fuel pump, installed a clear filter to see if the fuel was making it through, checked the heat shield, etc.). It baffled me for a year.

The problem was the alternator's voltage regulator. Hook a voltmeter to your battery (or through the cigarette lighter) while driving. As the engine heated, the voltage began to drop until it fell below 12.5... then the system begins to drain the battery. When it hits somewhere around 10 or 9v, the fuel pump isn't getting enough oooomph and the engine starves for fuel... making it look like a fuel pump/vaporization/etc. problem. A $100 rebuild of the alternator fixed the problem.

This may not be your problem, but it is an example of how elusive the problem could be if the obvious routes are exhausted.

I now have the voltmeter hardwired into the system to allay my paranoia of losing juice far from home.
Phil

Glori,

Your symptoms sound a lot like my first (78) MGB, in 1984. If your car has been stored so long there is a good chance it still has the famous (infamous?) Opus distributor. Most have been replaced by now, as they failed years ago. I would look here first.
Get in touch with the Sacramento Valley MG Car Club, the resources of a local Club are well worth having and will save you countless hours of frustration and many dollars. These are all people who love MG's, so you can make some new friends as well. The Club's web site is at http://www.svmgcc.org.
Paul Konkle

The coil can fail when it gets hot, check for spark when it won't start.
Paul Hunt

I thank you all for the advise, and have looked into 55% of the suggestions with no success yet and now she won't start at all. I sit at work and day dream of how to fix her, pull out my grimmie MG book to look up a new possible cause. so I thank you all for the help so far we will keep going on causes. my check off list:
cleaned all elec. leads
carb. ok no fuel flow problems
new rubber tubes all around
new spark plugs and wires
new clear fuel filter
fule pump is ok
iginition is new (last owner replaced it)
but I still have the OPUS dist. and will look in to a up grade.
alternator is orginal
and coil has no spark and I will get a new one in the AM. thanks agine
glori

Glori, how do you know your coil has no spark (i.e., what was your test)? Before buying a new coil, disconnect the distributor (neg) side of the coil, test the positive side voltage with the ignition turned on to "run". If approximately 12 volts, then hook a jumper wire to the negative side of the coil and touch to (good) ground, making and breaking the connection. If the coil is good, you should see a spark jump from the coil secondary lead to ground (3/8 to 1/2 inch or so). If this works, you need to look elsewhere. Align the rotor to the number one tower in the distributor cap and repeat the test as above, seeing if spark jumps from the number one spark plug wire to ground. This should verify that the secondary side of the ignition will at least run the engine.

Wayne
Wayne Pearson

now I have replaced the lucas coil with a new one didn't work, tested this again and no help, removed the distur. and it says lucas too, not Opus, and its been rebulit before by the looks of it and the striped screw heads. if this isnt the sorce it just needs a good rebulid on it anyways. I called a local MG club member and attempted to take notes and he rambled word I had to look up but Im getting there, thanks to all.
glori

Two coils no spark implies some other problem in the ignition LT circuit. You need to break out the voltmeter. Check the voltage on the coil +ve. It should be 12v with the points (do you have points?)open and about 6v with them closed. If you see both those then you should be getting some kind of a spark. Instead of checking for a spark at the plug leads remove the coil wire from the distributor and check that. If you still get no spark them maybe you did strike unlucky and get a bad replacement coil. If there is a spark but it is yellow and will barely jump a plug gap the capacitor has failed. You should get a blue spark, a sharp 'crack', and be able to draw it out to about 1/4". If that is what you get, but *still* no spark at any plug lead, then look in the cap and make sure the little spring-loaded carbpon brush in the centre has not fallen out. If that is OK try a new rotor arm, somethimes they seem to break down internally.
Paul Hunt

took your advice Wayne and surched the spark to the frozen drive dog of the distrubiter its in pices on my table with all the needed parts on the way from moss. I would like to get a better distruberter but I understand a larger hole needs to be drilled in the block, the nearest MG shop is 50 miles, and the experence will be good for my girls to see how to keep your calm when working with items that are dirty, grimmie and and broken.
thanks glori
glorianne

I got a new distributor from www.propermg.com.
The number is Lucas 41427 on their website -- you do not have to
drill a larger hole into the block (not sure why
this was recommended to you.)I have a 79 MGB
(same engine as yours) and this distributor gives
good performance without pinging.
The old distributor is probably worn out in
general, so a new one would be a good solution.
Ronald

This thread was discussed between 20/04/2002 and 27/04/2002

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