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MG MGB Technical - Su AuF 300 MGB 73 stopped chattering

Hopefully I am posting correctly this time.In the course of this last very cold winter my B conked out on two occassions running home.Noticed there was no noise from the pump.Strange because of late he had been constantly chattering,(non stop,not correct)(Previously,normally 2 or 3 times and then mission accomplished would wait for met to start motor.) However a quick tick with hammer stump and off it went;this repeated two days later at night ,very cold min min min temp.however repeated trick hammer and off we went home.Today however this became more serious.test drive for tommorrows mot and it died again and no matter what tick was administerd he would not beat.Pushed a kilometer home ,cursed many sleeping policemen.But what now? quarter tank petrol.Can he be removed? probably the only thing that has not been replaced (35 years old?) or should I do some checks?There was a lot of salt on roads through winter, and although I have been busy cleaning generally under the car the pump had stupidly not received more than cursory attention and has been laid up until yesterday when I drve some 30 kilometers. Any advice app. as work committmentsd are making severe inroads on my available research and brain time and would very much like to get one or two weekends out of M for the winter sets in again
Rangerprovo

I'm assuming you have an original SU fuel pump with points with the pump located on the lower right side.

The "chattering" you hear from the pump is from the points in the pump doing their job. Like all points, they eventually pit and wear down. The reason giving the pump a good "whack" will help temporarily is that it frees up the points when they are so pitted they're not able to open completely or they've managed to "stick" together.

You should probably replace the pump. Some people swear by solid state pumps, but as the old one has lasted 35 years, I doubt if some of the cheap plastic bodied solid state pumps would be as reliable as a new version of the old system. Burlen does have sold state version, though, that looks just like the old one, perhaps others can vouch for its long term reliability.

In a pinch for your next MOT appointment, you might take out the old pump, sand the point surfaces and reinstall if you'd rather not wait for a new pump. Instructions for removing and re-installing the pump as well as the points can be found in your friendly Haynes manual.

I've done the operation a few times, in one I removed the old faulty pump, installed a new one, but replaced the points on the old one as a spare. You do have to be aware of the possibility of fuel coming out of the tank. Jacking the car up at a steep angle should help, but have a portable fuel can and funnel handy.
John Zajac

Hey thanks for your feed back.Sounds like good advice. I like the idea of ordering a new pump, but as you say that could take a while;whereas if I open up the original and clean the points it might make for a good temp fix if nothing else. Yes I will find a can to have about
Rangerprovo

The resident fuel pump guru on this forum is David DuBois. He rebuilds them, and has a website full of good information about them to help you fix it yourself.

The advice you got on the points is good, but I have found it hard to do a good job of cleaning them with the pump on the car.

Also, I think the continual chattering when it worked indicates another problem. The pump should stop chattering when the fuel pressure is high enough, and if it keeps chattering I think there is a stuck check valve.

Here is David's website:

http://homepages.donobi.net/sufuelpumps/

Charley
C R Huff

No doubt good advice, Charley.

I hope I didn't give an impression of taking a file to the points in situ ("take the pump out" in my post). Filing, sparks, gas/petrol fumes don't mix!
John Zajac

Well, John, no back peddling required for my benefit.

Mine quit clicking while I was in Florida for a month, and I would have sanded them in situ if I could have. But, since I couldn't, I settled for just goosing them with my finger, which cured the problem.

Charley
C R Huff

The whack with a hammer 'cure' is for points which have stuck open, i.e. the pump stops clicking at all and the carbs empty. If the pump is chattering all the time i.e. a lot more than the initial few clicks when first switching on the ignition after being off for some time, and the occasional click thereafter, it means either you are out of petrol, there is a hole in the pickup pipe above the level of the fuel, or one of the one-way valves is stuck open. If a whack *did* stop it chattering it must then have been one of the valves, as it couldn't help with the first two. If it's been chattering a lot for a long time then the points are probably knackered now.

If you have a rubber bumper then the points end is in the boot and you can get at those just by removing the metal box and end cover. If chrome bumper then it is an under the car job, and probably removal. But in either case if refacing or replacing the points you should reset the throw of the diaphragm push-rod, which *will* require you to remove the pump from the car and separating the pump end from the solenoid end, and you also need to examine/clean the valves. On a rubber bumper the pump is above the top of the tank so as long as you keep the end of the supply pipe at the same level nothing will siphon out. But on a chrome bumper it is below fuel level and unless the tank is actually empty, or very nearly so and the car tipped at a very large angle to raise the right side and tiop all the fuel to the left-hand half of the tank (the pickup is in the centre for obvious reasons) you will get fuel siphoning out until you can disconnect the supply pipe/hose and lift the end above fuel level. Jacking the right rear corner isn't going to help much, that is for sender replacement.

Filing points won't create a spark, they aren't ferrous, but in any case I've never seen sparks off ferrous metal short of using a grinding wheel on it, or possibly belting it with a hammer.
PaulH Solihull

This thread was discussed between 01/08/2010 and 02/08/2010

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