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MG MGB Technical - runs well stop for 5 min runs like pig

1975 B. runs well for 10/20 miles then if you stop for 5 min car is difficult to start and runs like a pig, will not pick up any revs and nearly dies on incline. Have recently replaced fuel pump, fuel filter, lines and tank. All ignition new and head off for new exhaust valves. anybody ?
alan

Alan. Lot of data, very little information. The only things we know are that the car seems to start normally, run for a short period of time, then, performance declines.

Does N.I. stand for "Northern Ireland"? If so, what carb(s) are on the car and what distributor are you running? What happens with the tach when you have these problems? Does it drop to zero, then, pick up again (low tension ignition circuit problem) or wind down as it nearly dies? Do you have a vented fuel cap or do you have a charcoal cannister with the vent line from the tank going forwards to connect to it? Have you done a fuel pressure and volume check to see that the new pump is working correctly? Have you done a compression check? When was the last tune up and what do the points and plugs look like?

You need to check out the basic issues--ignition system and fuel system, in a logical manner and see how they are performing. You could have a coil that is bad and, as it heats up, it is not producing properly. You could have a weak fuel pump or a clogged tank vent. You could have the condensor breaking down under heat or a loose ground wire in the distributor. You could have the heater valve leaking onto the distributor cap and causing it to short out.

My website, www.custompistols.com/ has some tech articles on the MG section. Dave DuBois has some good articles (one new) on trouble shooting the fuel system and the SU fuel pump which includes pressure and flow figures. I have ones on compression testing, ignition system trouble shooting and timing. All of these may be of use to you and will allow both you and us to focus on what might be the problem in a more directed manner.

Take a look at your engine and see if the fuel line is routed properly. See if the heat shield for the carb is in place and in good condition. Pull your plugs and look at the color and see if they are fouled. All of these will help to determine where the problem might lie.

Les
Les Bengtson

Alan: Does it backfire through the carburetors? Does the tach "bounce"? If so, it is indicative of electrical. Sounds very much like the condensor in the distributor. It is a cheap item to replace. In fact if you have a spare from a used points set, go ahead and use it. If this does not solve the problem, you obviously need to dig deeper, ie: secondary coil wire perhaps.

Without any shop manuals or the like, I've learned to replace the cheap items first. Very often therein lies the solution.

Let us know how this issue gets resolved.

cheers

Gary :>{D
gnhansen

Hi Alan.

My first thought is vapour lock.
I would take it on a run, stop and open the bonnet (to avoid underbonnet heat build up), wait for 5 minutes with the bonnet open, close the bonnet (!) re-start and see what happens.

Don
Don

Does the problem clearup after you run it for awhile? If so I bet it's vapor lock and it can take sometime to get rid of the problem.
Mike MaGee

This thread was discussed between 21/08/2005 and 22/08/2005

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