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MG MGB Technical - Fuel supply blockage

Hi all,

The latest problem with my 73 BGT is its new habit of shuddering to a halt. It happens in exactly the same way as when I run out of fuel, except that I KNOW that there is plenty of fuel in the tank. It often happens when I am driving up hill. On one occasion I coasted over the hill and was able to restart the car on the other side. I suspect that fuel supply is the problem, and that specifically I have a blockage in the system somewhere. How can I find where the blockage is? How should I approach this problem?

Any ideas gratefully received.

Andrew
Andrew H

It's probably in your tank - the blockage that is. A buildup of at least 20+ years of crud and sediment. Try disconnecting the fuel filter and the ouput line of the fuel pump and give it a shot of compressed air but do place a bucket under the fuel line to catch the fuel and see if anything comes out. If nothing comes out it's most likely in your tank. BTW, there was a TV show in which the murderer placed a ball of some sort in the victim's gas tank and after a few minutes of driving the car would stall and then the murderer would then pounce on them.
Mike MaGee

I've been repeating this a lot lately, so I'll keep it brief. I had a similar symptom: Pointing up hill, tank at 1/4 or less, car would run out of gas. Turned out my replacement tank had a leak in the pickup line inside the tank. I sealed off the existing line and replaced the sender for the later style with the integrated supply tube.
Matt Kulka

Tank is virtually brand new so I think Matt's idea is more likely. Matt: how did you establish that this was the problem?

Does anyone know how much space there is between the bottom of the outlet pipe and the floor of the tank?
It is a repalcement for a UK specs 73BGT.
Andrew H

Mike --

Can you give any more information on that ball?

glg

Andrew,

I ran the tank down to about 1.5 gallons, then pulled the sender off to have a look inside. I could see the end of the pickup tube was still immersed in gas, but the pump would only pump air.

I worked from the front of the car back, isolating items. First, found no fuel at the filter input, then found no fuel at pressure regulator input, then found no fuel at the pump output, etc. until I was down to sucking on a (clear) piece of hose connected to the flare fitting on the tank. And no fuel would come through. So this told me the problem was in the pickup tube.

I verified this by reconnecting the rest of the system, but instead of connecting the hard line to the flare fitting at the tank, I put the rubber hose on the tank end of the hard line, and the free end of the hose in a jar of gas. Viola, fuel pumped through the whole system.

One interesting point - while sucking on the rubber hose all I could get were fumes, when I blew through it, I did get bubbles at the end of the tube in the tank!

I hope this helps,

Matt
Matt Kulka

If the problem *is* sucking air then the pump would be chattering away like billy-o as if you *had* run out of fuel. I know you say "exactly the same way as when I run out of fuel" (a frequent occurrence?) but I'm not sure whether you are referring to just the 'shuddering' or the chattering as well. If it is not doing this then it is more likely to be a blockage, one between pump and carbs would stop it pumping altogether, one before the pump might cause it to click faster than normal but not as fast as being out of fuel. In any event, when you come to successfully restart the car the pump will chatter for a few seconds while it is filling up the float bowls again. If it isn't doing that then the problem is unlikely to be fuel related. All this pre-supposes an SU pump, of course.
Paul Hunt

I was getting a bit poetic with the shuddering, the point was that the engine (not the pump) sounds the same as running out of fuel.

As for the fuel pump I will listen more closely. Generally it chatters away, apparently at its own volition. Its noisier when the tank is low, but sometimes its just noisy anyway.

You say: 'a blockage ... between pump and carbs would stop it pumping altogether'. Does that mean such a blockage would leave the pump completely silent?

It looks like a very old pump and the hoses that connect the pump to the copper tubes look tatty. One of the brake lines to the rear were replaced recently and I think the fuel pipe runs next to the brake line at some point - I want to make sure there is no kink in the fuel pipe.

However all work has to wait until weekends with these short days.

Andrew
Andrew H

Andrew,

Paul makes a good point. In my case, I had an aftermarket pump which simply whirred at all times, regardless if it was pumping air or liquid.

For a normal pump, you have it correct. A blockage between pump and carb would cause the pump to go silent.

To restate Paul, a normal pump will click faster and more loudly when it's sucking air.
Matt Kulka

Whichever pump you have it should be capable of delivering at least one pint per minute with a pipe removed from a carb and directed into a container. Another recent thread had the original poster realising that when he was going up hill and had the problem he also had the throttle hard down, so it was more a case of throttle opening than being on a hill. This can be simulated for short periods by driving along the flat at full throttle with the brakes on.
Paul Hunt

This thread was discussed between 19/11/2003 and 21/11/2003

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