MG Car Repair/Weak SU fuel pump
QUESTION: I have a 1980 MGB. Installed a single, new SU carb. After car sits for a week or more, after starting up, it stalls out and won't restart, I remedy this by removing the gas line on the carb, turn key to activate electric fuel pump, which refills the line to the carb, reconnect, and the car starts and runs fine. How do I remedy this problem? Note: The fuel filter mounted on the firewall is several inches above the carb gas inlet connector...maybe the problem....really don't know. Thanks.
ANSWER: Hi Will
This is not vapour lock. Vapour lock only happens when the gas in the line or in the float chamber gets so hot that it boils. You are having trouble starting a cold engine.
I think your problem is either a lazy fuel pump or the fuel filter is positioned too high, or both.
Next time you go to start your engine after it has been sitting for a few days, turn the ignition key to the running position (Red ignition light should come on) and do NOT operate the starter motor. Just listen to the fuel pump. It should give a quick healthy Brrrp as it fills the gas lines, then it should slow, and then it should stop ticking. At this point, you can operate the starter motor and the engine should fire and run without stalling.
This starting technique may be all you need to do to solve the problem. It is only necessary if the fuel lines have drained because the car has been unused for a while.
If the pump did not give a quick Brrrp but just a slow chug, chug, chug then you need to service the pump. On a 1980 MGB the lid is accessible within the boot (trunk). Take the lid off and clean the points with a strip of emery cloth. (Steal an emery board from the bathroom. They work just as well on points as they do on finger nails).
If you regularly leave your car for a week or more, then I would advise you to consider replacing the points with an electronic conversion from Burlen Services of Salisbury, UK. No more dirty points to worry about.
---------- FOLLOW-UP ----------
QUESTION: I do know how to access the fuel pump thru a 4" cube shaped metal box located inside the boot (as you've said). I do not know exactly where the "points" are. If you might either send me a sketch or a worded description of exactly where these points are, I will greatly appreciate it. The Bentley manual I have for my car is not very detailed on the fuel pump. Thank you in advance.
Remove the black cube to reveal the top of the pump. There is a white wire connected to it. Disconnect the white wire and undo the 2BA nut (29) holding the terminal. Remove the terminal (28). Careful you don't drop the spring washer (27). There may be a second nut underneath it. If so, remove that nut also. Now you can remove the black plastic lid of the fuel pump. It may also have a ring of sticky tape sealing it, which you must also remove.
Lo and behold, you have found the points. On a 1980 MGB they will probably be double points. Carefully lift the points and slide the emery board into the gap. Let go of the points and they will close together under their own spring tension. Slide the emery board in and out a few times to clean the points. If they are badly burned you may need to fit a new set of points, which is a more tricky operation.
Put everything back together and the pump should now sound much quicker and more powerful.
I have attached an exploded diagram of an SU fuel pump, courtesy of Burlen Fuel Systems. Yours is similar but not identical.