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MG Midget and Sprite Technical - Fuel delivery problem after vigorous drive...

Hi folks,
Here's what's happening with my '76, 1500. I had a fuel problem last Fall and replaced the mechanical pump. I finished the season strong, after that. Now, this Spring, after driving for 20 minutes or so, the engine dies. I can see the lack of fuel in the in-line filter. I've been sticking close to home, so as to avoid any lengthy tows. So, the past couple of times, I was within a street of my home. I walked home, got a gas can, screwdriver and eye-dropper. Pulled the line going to the carb, eye droppered about 10 droppers of gas into the line and powered back to my garage. What I've noticed hours later has me puzzled. The gas filter goes from just-about dry, to COMPLETELY full. I never see it like that. It's like I'm pulling a vacuum or something and over a matter of time the gas filter fills up. I drilled a small hole in the gas cap a couple of years ago. Today I even drove around with the gas cap cocked open, just in case. It happened anyway. I have another mechanical pump, but I'm hesitant to put it on in case that's not the problem.
Any ideas ?
Paul W 1976 1500

I had something a bit similar. It would run for a while then splutter a bit before cutting out. Leave it 15 mins and it would run fine.

It took ages to track down and turned out to be sediment (rust particles) in the tank's pick-up pipe.
I only found it when I took the tank out and sucked when I meant to blow to see if it was clear!

My knowledge of fuel pumps is limited but, if it has a diaphragm driven by a spring, I suspect there's a residual suction in the system that is pulling fuel past or through the blockage slowly while the car's stationary.

Have you got any (safe and hygenic!) means of applying suction at the tank outlet? - a bike pump might do it. You might need to reverse the cup washer to get greater suction.

Colin
C Mee

Thanks Colin, I'll have to have a look. Do I need to drop the tank? I haven't done any gas tank stuff. Of course, it's still quite full as I store it with a full tank.
What you're saying makes sense. I don't see any kind of particles in the fuel filter though.
Paul W 1976 1500

Does the problem occur with a full tank or only with the tank about 1/2 full. The pick-up in the tank can get damaged or rust and is not a problem with a full tank as the pick-up is below the fuel level but with less fuel a leak in the pick-up tube can be exposed and result in a lack of fuel to the engine.
David Billington

Paul

I had taken the tank out to give it a thorough inspection and to check the gauge sender when I found the blockage. I don't think it would be too difficult doing it with the tank in place.

I'm not sure what the original pipe arrangement is, I suspect it's steel tube which might make it a bit awkward. On my car, the PO had replaced the pipe from the tank to the rear-mounted electric pump with rubber hose that was jubilee clipped onto the stub of metal pipe left at the tank connection.

C
C Mee

Right now Dave, the tank is 3/4 full.
I'll have to crawl under there and see what's coming out of the tank. Perhaps there's a rubber line at some point and I can take it apart there and put some pressure into the tank. I might even be able to get enough pressure to the tank from under the hood. That's a long line run though, I don't know.
I was thinking I could find an old tire nozzle, hook that up to the fuel line. That would make it easy to get some pressure in there with a pump or compressor.
Paul W 1976 1500

Paul:

I have a 1972 midget in Tonawanda, NY and have observed a similar issue. At times, the see thru plastic gas filter (inline under the hood) looks empty yet the car idles and runs fine. Other times, it fills vigorously. Still no change in performance, etc. I change this filter each spring when taking the car out of winter storage.

My electrical SU fuel pump is under the car near the fuel tank. I have NOT dropped the tank for any issues in the last 15 years of ownership.

My first suggestion is to use a vacuum gauge (which can also measure low pressures when used inline) and get an idea as to fuel pressure at either start up and/or idling in the driveway.

Another suggestion would be to use one of those plastic over sized soda bottles to get a measurement of fuel volume and consistency of flow.

Plan B is to invest in a AAA auto club membership and keep your cell phone handy.


Mike P.
Mike Pelone

Check for any leaks in the line between tank and pump. In particular check rubber hoses. They can develop tiny cracks. This may well not show as fuel leaks on the pipe either because fuel evaporates too fast or because there is not enough head of fuel in the tank to open up the crack. But when driving at speed and the pump is working hard and has been doing so continuously for a while then air is drawn into the fuel line with the pumped fuel. This causes fuel starvation which may seem to cure itself after a few minutes rest. And it may well also appear to fill any clear filter with air.
GuyW

Well, I picked up a nice little pump at Walmart and drained the gas tank. I pulled the line off the tank and put a little baggie over the end of it. I hooked up my bicycle pump on the fuel line under the hood and pumped the line. The baggie had cloudy gas in it, but no visible sludge. I reattached the line on the tank, put some gas in and pumped it up again. I could hear the gurgles in the tank. Put it all together and just gave it a good ride. I've got a road a couple streets over that I can get up to 50mph on. So I went around this big block 3 times. So far, so good. I could feel the engine starving a little bit before at high speed, now I don't feel that. There must have been something going on with the line. Feeling pretty road-confident now.
Paul
Paul W 1976 1500

Paul,
(where legal and safe to do so of course) you should be able to go at a lot more than 50mph all day long without worrying about the fuel pump. Not driving the car for a matter of weeks, let alone months, isn't the best for the whole car including engine, brakes, suspension, etc., etc. and fuel delivery.

Now you've got confidence in the car running again why not, if you've not already done so, fully service the car then fill the tank and add a fuel system cleaner and take the car on a sustained high speed run (after fully warming the whole car up of course). Take the car about 30-50 miles on a constant legal high speed road or regular roads where you can often drop a gear and accelerator fairly hard for a distance and/or accelerate up steep hills.

Give the car what's called a blow-out run or "Italian tune-up" (run) and enjoy the journey.
Nigel Atkins

If the fuel that came out of the line was cloudy as you say, maybe there was a bit of water in there, which in turn will not pass through the filter and restrict flow, giving the fuel shortage symptoms you had earlier

An old trick is to put a couple of cup fulls of methylated spirits in the tank with the petrol and that will get rid of the moisture

willy
William Revit

This thread was discussed between 01/06/2018 and 08/06/2018

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