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MG MGA - FUEL PROBLEM

Back home,just barly after my fuel supply was interupted. Apparantly I have a fuel starvation problem. The diagram below shows my setup and while it was still pumping I could see gas coming from the tank into the filter (sporatically) and I could see gas sputtering out the front hose by the carbs. I disconnected everything to check it out and as a result I now have no suction at all. The pump ticks over rapidlly but produces no fuel.

**** fuel lines cleaned out****pump cleaned out****fuel tank disconnected and alternate fuel supply tried****ground is good******pump is getting power*****no over heating*****no air leaks that I know of*****half a tank of gas**** new clear palstic filter installed facing the right flow direction****all this but no gas.

Two things that are interesting #1 the rapid ticking of the pump and #2 I do not know what to look for when verifying the diaphram. Anybody got an idea?


Gordon Harrison

Rapid ticking usually means no fuel getting to the pump chamber, is there any in the tank?

dominic clancy

Hi Gordon,
I would try eliminating the filter and running a direct line from the tank and see if that cures it. If it is an SU fuel pump, they say you should never put a filter between the tank and the pump.

Good Luck,
Ralph
Ralph

Gordon - You state there are no air leaks that you know of - are you certain of that? The pump running rapidly, continuously is a classic symptom of an air leak. Here are some tests you can run on the system that can isolate the problem:
If the pump is ticking rapidly all the time, the problem is going to be an air leak on the inlet side of the pump. This sort of a leak is not likely to show up as a damp spot anywhere as the fuel on the inlet side of the pump is not under pressure at that point. Places where the leak might be are: the pump diaphragm, compression fitting on the fuel line to the banjo fitting itself, crack in the fuel line, compression fitting on the fuel line at the tank, a fractured braze joint attaching the fitting to the tank, or a hole in the pickup tube inside the tank (fill the tank all the way to the top to check this possibility). To troubleshoot this situation, disconnect the fuel line from the carburetors and direct it into catch vessel of some kind and turn the ignition on and check for bubbles in the stream of fuel - bubbles will indicate an air leak. Next, remove the fuel line from the pump (disconnect the line the fitting at the tank to prevent siphoning fuel from the tank when the line is removed from the pump) and replace it with a flexible line leading into a container of fuel, then rerun the first test. Bubbles in the stream of fuel indicate that the leak is in the inlet side of the pump or possibly the pumps diaphragm itself. No bubbles indicate the leak is toward the tank. While you have the pump taking its input from a can of fuel, run the output of the pump into a container marked at the 1 pint level. Start with no fuel in the catch container, turn the ignition on and time how long it take the pump to deliver 1 pint - should be less than 1 minute. If it takes longer that that, you pump is in need of work. Replace the normal fuel line to the pump and move the flexible line to the tank end of the line and rerun the test - bubbles indicate the leak in in the line, no bubbles indicate the tank fitting or pickup tube.

On the subject of your hook up - you should move the filter to the outlet side of the pump. A filter on the inlet side of the pump will not harm the pump in normal operation, but if the filter becomes clogged to the point that it stops fuel flow, it will cause the pump to stall in a current on condition and if the power is left on (such as during troubleshooting) it will burn out the internal swamping resistor. This will not stop the pump from operating normally once the clogged filter is replaced, but the burned out swamping resistor will cause the points to burn prematurely. Perhaps worse, if the burned points are replaced with a new set, that new set will also burn out prematurely. This is the reason that I caution against putting a filter between the tank and the pump and probably the reason that MG never put on there to start with.

The SU fuel pump are pretty much immune to small amounts of rust particles, as are the SU carburetors (particularly the earlier H and HS types). Both the SU carbs and the SU pumps have relatively large openings in them and can tolerate more debris, unlike more modern carburetors with very small jets that will get clogged up by very fine particles. If there is no rust in the fuel tank and lines, there is no reason to need a filter. There are filters on the pickup tube in the tank and the SU fuel pump, both are fairly course, meant to stop rocks and small birds and will not clog easily. The same cannot be said of modern, high efficiency filters, they will stop very fine debris and can clog rather quickly. If rust particles start showing up in the pumps or carburetors, it is time to find the source and eliminate it rather than treating the symptom with more filters. Cheers - Dave
David DuBois

I had a similar problem, it turned out to be a blockage in the tank 'pick up' pipe.

I removed the tank and back-flushed through the pipe between the tank and the pump.

JB
John Bray

Gordon, when I had a similar problem it turned out to be crud in the pump valves. Not so likely to be your problem as you have a filter in front of your pump, but it might be an idea to rule it out. If the valves are not seating, the pump just shunts the fuel forwards and backwards, so nothing gets to the carbs and the pump just keeps ticking.
Lindsay Sampford

Domenic,Ralph,Dave &John,
Thanks Guy's.....The tank is half full,the filters I use are clear and get changed about every two months,( but I will replace them between the pump and the carb)....from an alternate fuel can to the pump,key on ,no gas at the carb hose yet rapid ticking of the pump. All the joints and connections have been gone over. rapid ticking / no gas.

Could you tell me what I am looking for when I dismantle the pump and look at the diaphram? Is the replacement of the diaphram a simple affair or does it have to be tune in conjunction with the points of the pump?
Gordon Harrison

Lindsay,
The valves appear,to my untrained eye to be OK. I am more on the lines that it's the diaphram. I am going to put in one of the little facet pumps to get around. Maybe it's time to sent my pump off to dave for a check-up,althought it is only 3-4 years old.
Gordon Harrison

Hi there
Gordon diconnect the pump intake hose and replace with hose going to your spare gas tank siting on floor close by. That will tell you where to look.

Martin
sharpeys

Gordon - You have e-mail. Cheers - Dave
David DuBois

This thread was discussed between 09/05/2011 and 10/05/2011

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