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MG MGA - strange problem

Hi all,
I need your advice for a strange problem.I will tell you the complete story, maybe it is relevant.
A few weeks ago I drove back home with the MGA and it started to miss a few times and it went worse with every km I dove. At home I changed the condensor, made a test drive and everything looked OK.A week later I went to a car meet. On the way to the meet the car drove perfect. On the return I had to stop for some traffic lights and when I released the throttle the car started to back fire and then stopped completely.After ten minutes the car started but after 100m driving the same happened, back fire and stopped. So I changed the condensor again and I got home without a problem(100km motorway at 100km/h).
I had it with the condensors and a few days later I installed an Accuspark electronic distributor and cleaned the float chambers. Car started immediately, I timed the ignition and made a test ride. The car drove perfectly untill I had to stop for some traffic lights. Suddenly I heared a sharp clicking(3 or 4 times) from the fuel pump and a that moment the idle RPM dropped from 850 to 500 rpm and the engine wanted to stop. I pushed the throttle and the idle came back to 850 rpm. No problems anymore untill I drove the car into the garage and the same happened again. So next day I changed the fuel pump,changed the coil, changed the distributor(new points,new condensor) and made a test drive. Perfect.
Last week I made a four day trip with the car in very hot conditions and he performed perfectly. Untill I got home. When I drove the car in the garage I stopped and suddenly I heared the fuel pump from his normal ticking change in a sharp clicking(3 times) and at the same moment the idle dropped from 850 to 500 rpm and if I did not pushed the throttle I think he would have stopped.
So I try to understand the relation between the fuel pump that starts to click fast for a few seconds and the drop in the idle rpm.A drop in the idle from 850 to 500 rpm means to me a fuel problem but I can not understand what the fuel pump has to do with it.
Any help or advice is more than welcome.
Regards,
Herman
H. Jorens

Herman
The pump clicking fast means fuel is escaping somewhere
If the idle drops at the same time it is most likely one of the carburettor float needles is sticking or some rubbish is getting under the seat of the needle
does the car have a fuel filter-------
William Revit

Fast ticking of the pump can also indicate that the fuel in the tank is not getting to the pump - or that the tank is empty.....

I have learned to be very aware of pump noises over the years and have on occasions put 45 litres of fuel in the tank!
Dominic Clancy

If there are any rubber hoses before the pump, replace them. Age can cause tiny cracks that are enough to let air in, but not liquid fuel out. So you will never know anything is wrong until the pump loses suction. Also make sure the intake inside the fuel tank isn't blocked with rust. This can cause intermittent loss of power which corrects itself after sitting for a moment because the rust flakes fall off once the pump stops.
Steve Simmons

Thanks for the comments.If there was rust at the intake I think the car would not run fine at 70 or 100km/h. It only has a short peace of rubber between the end of the copper fuel pipe and the first carb.
But it did not had a fuel filter untill a week ago.I found a small amount of very fine rubbish in the float chambers.I cleaned the needles but not the seats.
I will replace the rubber hose and open the float chambers to clean everything again.
Is there a possibility to clean the passage between the float chambers and the jets?
H. Jorens

What is the pipe between the tank and the pump like? Is it steel or copper?

On my MGB, the original steel pipe developed a pin-hole at its highest point and was sucking air.
Dave O'Neill 2

Herman

You also need to check the integrity of the metal pipe from the tank to the pump. I once had a pin hole in this, incidentally caused by it shorting on the battery terminal. Certainly sounds like a fuel delivery issue.

Paul
Paul Dean

The car will run fine at any speed despite rust in the tank. It accumulates on the intake screen gradually, and eventually blocks the intake. When you switch the car off, the rust flakes fall off and you start all over again. I'm not saying this is your problem but it could be. I've seen it many times on all different vehicles. If there is no intake screen then you may want to check the filter screen inside the pump. I saw a pump burn out once from this screen being blocked by rust.
Steve Simmons

Hi Herman,
I can't add anything to the comments you've already received about the fuel pump, but a couple of years ago I had major condenser problems, replacing it 3 times in a year. My experience was similar to yours, with everything being fine for 40 or 50 miles before it started misfiring and eventually stopped altogether. Sometimes, after letting it sit for a couple of hours it would restart, for the same thing to happen again after another 40 or 50 miles.
The solution for me was to fit a yellow wire condenser instead of the orange wire version. Original Lucas condensers had 3 metres of winding inside, but the orange ones have between 1 metre & 1.5 metres. The internal bonding & construction also leaves a lot to be desired. After fitting a yellow wire version I haven't had a repeat of the problem.
Robert

Robert Sinclair

Well, sometimes you need to check the fuel filter in the SU pump. This brought me to a complete stop during a drive last fall. Easy roadside fix but embarrassing. It did its job. The carb filters were pristine. Jud

J. K. Chapin

I had a similar problem when I first bought my MGA. It would run fine and then start to cut out a bit and then it would get worse and quit running. When I waited 10-20 minutes or so, it would start and run for about the same length of time and quit again. My first thought was fuel pump, as the car had a Harting pump on it. Anyway, after fooling around with number of ideas, I discovered the coil bracket had worn a hole in the coil, allowing the oil to run out. When the coil heated up it quit working and when it cooled off, it worked again for awhile, until it heated up again. The Harting fuel pump is still working 20 years later. Another idea to consider.
Bill Haglan

Hi all, thanks for the comments. I replaced the cheap condensor with one I bought in a car shop. The coil is a new one. Points are new. The first problem I had was indeed an ignition problem that is solved now. The problem I still have is a fuel problem I think. The filter at the end of the pick up pipe is difficult(impossible) to check in a MGA. The fuel lines are copper and only a few years old. The pump is a Hardi that I replaced with a new one to eliminate that possibility.
As soon I have the time I will open the fuel bowls again and remove the needle valves again but also the seats(I did not removed them the first time) and clean everything. I also discovered that there is no mesh filter and spring behind the banjo bolt at the inlet on one of the two carbs(carbs rebuild by a known UK company). I will order one and install it.
I am just wondering it there can be some dirt between the the fuel bowls and the jets and if so it it can be cleaned without disassembelling the bowls from the carbs and removing the jets. The bit of dirt I found at the bottom the bowls was more like a very fine brown mud so I suppose that the dirt will pass the jets like the Guru says.
Thanks for the comments and will keep you informed.
Herman
H. Jorens

Compressed air is your friend. You can blow it into the jets (watch for gasoline flying at your face) and also blow the hard lines out including the one into the tank. But if the problem is crud on the intake screen then this is only a temporary fix. The tank will need to be cleaned. If you have a drain plug, this is a good way to start. Drain it and see if any crud comes out.
Steve Simmons

This thread was discussed between 30/07/2019 and 02/08/2019

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