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MG MGB Technical - Fuel pump ticking far too much

I have a replacement fuel pump, not sure of the make but made in Germany and has a blue cap over the 'points'. When the ignition is turned on the pump ticks to fill the fuel bowls then goes quiet. When running it ticks away at quite an alarming rate (once or twice a second) and even more so when I accelerate (although not hard as I am still running in the engine). There are no fuel leaks. It's getting really annoying now and I was wondering what areas to look at first. This occurs when the tank is almost empty as well as when it is half full.
Steve Church

Characteristic of air leaks on the suction side, and they will not usually leak fuel. Lower the fuel level, the harder it has to suck, so it gets worse. ?Remote possibility that there is a pinhole rusted in the pipe inside the tank.

FRM
FR Millmore

Is the pipe inside the tank removable for inspection? I've not been under to examine where the pipe exits the tank. I'll check that tomorrow. Can I dismiss the likelyhood of a pump fault? The pump looks like a recent replacement by the PO so maybe he had similar problems that he thought were pump related. There were three spare (used) SU pumps in the boot when I got it.
Steve Church

Not om early cars; later it is built into gauge unit. Possible threaded connection at the tank is damaged, remove and examine. Hook back up and check pump output for bubbles by putting a hose in a jar - should be none. If so, then: attach a piece of rubber hose to the pipe to pump and put it into the tank; check for bubbles. If no bubbles here the pump is good, the tank pipe is bad.
Pumps usually do not fail this way; they can have a leaky valve, but will not have bubbles.

FRM
FR Millmore

While I am not familiar with the newer Hardi (blue capped pumps), if they have a large dome shaped cover held in place with a single hex head screw opposite the side where the inlet/outlet ports are, the gasket under that dome cover sometimes shrink, causing an air leak at that point. You can also get a leak around the inlet/outlet ports where the Banjo fitting goes, particularly if the ports have a recess for an 'O' ring and somebody puts a fiber washer on that side of the banjo. See the article, New SU Fuel Pumps with 'O' Ring Seals in the SU Fuel Pump Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Disclaimer: All the above goes out the window is the aftermarket is not designed the same as the SU pumps used on the MGBs. Cheers - Dave
David DuBois

I did a flow test this afternoon and could not see any bubbles in the jar, but I have an inline filter and could see bubbles entering it. I had a look at the fuel pump and there appears to be some staining on the endplate. So it could be an iffy inlet connection. The pipe (copper) goes to a union on the tank near the sender unit. Is this replaceable? (1968 vintage).
Steve Church

Pipe in the tank is hard to replace, as it is brazed to the tank, I have had issues with the threads on repro tanks and fittings, causing air leaks at the coupling. Fixed with a needle file and antiseize on the threads so it could be tightened properly. Study Dave's site and get to understand how the pumps work - your late Hardi is probably very similar if not identical.

FRM
FR Millmore

I will again state that I am not familiar with the newer Hardi Pumps, but as Fletcher states, the older Hardi were nearly an exact clone of the SU pumps.

You can't base anything on what is happening in a filter housing. They maintain a large bubble inside them that never seems to decrease. On my test site, even though the filter maintains a bubble, no air bubbles occur in the measurement chamber while the pump is running. After a 24 hour run, the filter housing is completely full of fuel, with no air bubble - go figure.

Bottom line - if the engine is getting sufficient fuel, is not overflowing and the stream of fuel is not full of bubbles, everything is working as it should. Cheers - Dave
David DuBois

This thread was discussed between 27/07/2012 and 29/07/2012

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