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MG MGB Technical - Sputtering problem

I just bought my 1975 MGB with SU carbs. I had a problem getting home from Maryland, 650 miles. It would run fine then all of a sudden sputter and lose power and I would have to pull over. I thought it might be the fuel pump or the carbs or something electrical. I am not sure if maybe the carbs are getting too hot and messing up the mixture.

This mainly happen on a 100 degree day at 60-65 mph. When I ran at 70-75 the car ran better but still a little rough.

Since I got it home it has died twice on me again where I had to pull off the side of the road. I've waited a little while then it would run fine until I got home.

I am very perplexed. The needles on the carbs were recently replaced and the car is in excellent overall condition with a recent restoration (new wiring harness, rebuild engine/carbs, etc).

Thanks in advance for you help.
Brian Kissinger

Alright, more trouble shooting. The car runs rough on start up, blows black soot/fuel-smell out the exhaust. Running rich?

Newbie MGB owner... Do I need to adjust the carbs? How do I do that?

Thanks in advance.
Brian

I once had a similar problem with mine. It turned out to be fuel vapourisation in the fuel lines near the carbs/exhaust manifold. Heat was vapourising the fuel and causing an uneven fuel feed to the carbs. It may be that at higher speeds, enough air is flowing through the engine bay to cool everything down and stop the problem.

The problem should occur at lower speeds though, when there is little cooling air heading through the engine bay. Does the car do this when hot and in traffic too?

Resh
S R Ellawala

Read the thread "76 B dies when it's hot", over in 'General'shounds very similar, maybe it will help
Bruce

Hi,
When I got my 73 B from the previous owner, it did the same thing and stranded me out on the highway a few times. I found out that the fuel pump was not a low pressure one but rather a pump with a higher pressure setting made for an American car. It simply overpowered the floats in the carbs and flooded them until the car loaded up and ran so rich that it stopped. After a few hours of sitting it would run fine again until the next "flooding" Finally found the problem and installed an SU fuel pump - has been running great. Alan
Alan

Before you look at the carb situation, have you eliminated the ignition as a source of the problem. Could be something as simple as the heater valve dripping on to the dizzy.
Paul K

If the tach flickers and dies at the same time as the engine it is the ignition LT e.g. coil, points etc. Use a timing light to see if the sparks are erratic or missing when it won't fire up again. A blocked emissions pipe can cause fuel starvation, if removiong the fuel filler cap results in a large 'whoosh' that is it. Setting up carbs correctly is not difficult but must be done with care and patience - and after any problems with the ignition have been resolved - see http://www.mgb-stuff.org.uk and click on 'Spanners' and 'SU Carbs'.
Paul Hunt

Great info. Thanks everyone. I cleaned out the floats and seems to fix the problem, for now. I do have an intermittent fuel pump problem. The car will die on me then I tap the pump a few times and it works fine. Fun owning a MGB, eh?
Brian

FWIW I chased a similar problem for months. It was caused be a lump of rubber in the float chamber inlet pipe. I believe the metal pipe had gouged it out of the fuel line when it was put back on following the changing of the float needles. It would block the inlet, stop the car and then fall back out of the way once the fuel pump was switched off. Because it was in the lid, changing the lines (twice!) didn't help.
The fuel pump one is a common issue, particulary if the car is used infrequently. Fortunately cleaning the points contacts inside usually sorts it out for the next twenty years. Otherwise a sharp tap with an Abingdon Special Tool wakes it for a while, up as you've discovered!
Steve Postins

This thread was discussed between 03/08/2002 and 09/08/2002

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