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SU AUB 662 Fuel Pump?

Posted by GlenP 
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Glen Phillips
DFW, TX, USA   usa
1972 MG Midget "Annabelle"
1976 MG MGB "Guinness"
1977 MG Midget "Widget"
My '72 Midget's fuel pump quit working; still making noise so it was getting power, but there was no fuel at the Weber carb. Tried the mallet tapping trick - nada. I pulled it and found it's the subject pump. Never heard of it. It seems similar to the late 1275 pumps. A Google search led me to a Moss stock number of #377-161, but it's listed as a 'special fitting' and not for US Midgets. It is used on a variety of other LBCs - Jag, TR, AH, Sunbeam, et al.

I called Moss' tech rep and we came to the conclusion that it's a clogged internal filter, a torn diaphragm, or a leaking intake hose that's sucking air. I pulled the pump apart and the diaphragm was intact and the insides clean as a whistle (Go SeaFoam!). There were no visible leaks from the fuel lines, so I'm now assuming that the intake line from the tank is open to the air. I'm going to get new lines tomorrow and hook everything up and see what happens.

The pic shows the pump just after I pulled it. Note the unidentified barbed fitting which I assume is for a vent line of some kind. This fitting was rotated to the back and not visible, nor was anything hooked to it. I did find a loose tube hanging off the wiring bundle and I'm thinking this hooks up to the fitting.

There is also a vent line at the end of the pump where the hot lead is. It's listed as a one-way valve and has a small ball-bearing in it. Blowing into either vent results in air coming out the other. Is this a means of bringing in outside air to the electric side of the pump and purging it to the fuel tank? Is if for simple venting or cooling air for the electrics?

Any hints or tips as to what this pump is about and how it's supposed to be hooked up? I can't find anything in the manuals or on line. The car did seem to run ok with it.



fuel_pump3.jpg    41.9 KB

ddubois Avatar
Dave DuBois
Bremerton, WA, USA   usa
Glen - The pump you have is a AUF 300/AZX 1300 series pump. It is one of two electric, SU pumps used on the Midgets. The AUB 662 number you see on the pump is just the casting number for the aluminum pump body. See the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: for tips on finding where the problem might be in your fuel system. Also see the article SU Fuel Pump Vents article to see how the vent should be routed. The pump should be oriented as you show it in your picture for the best performance (outlet fitting up and pointing to the left if viewed with the end cover of the pump pointing toward you).

An air leak on the inlet side of the pump will not show up as a line or fitting dripping fuel, but will interfere with fuel being pumped properly. To check for such a leak remove the fuel line from the carbs and route it to the bottom of a glass jar, turn the ignition on and watch the stream of fuel going into the jar. If the stream is full of bubbles, then there is an air leak. Remove the line from the tank to the pump (loosen or remove the line from the fuel tank first to remove stop any fuel from siphoning out of the tank) and replace it with a flexible line that can be dipped into a can of fuel. Once again turn on the ignition and observe the flow of fuel into the jar, watching for bubbles. If no bubbles occur with this set up, then the air leak is in the line to the tank or the pickup tube in the tank. If there is still bubbles in the outlet stream, then the pump has an air leak in it, most likely the gasket under the large domed cover held in place with a single hex head screw in the center. Finally, if the pump is still not pumping fuel, you may have a fractured reed valve in either the inlet or outlet side of the pump.

Dave DuBois
1953 MGTD
1966 MGB

Member Services:
SU fuel pump restoration and conversion to solid state. Information and technical articles on SU fuel pumps.
Glen Phillips
DFW, TX, USA   usa
1972 MG Midget "Annabelle"
1976 MG MGB "Guinness"
1977 MG Midget "Widget"
Thanks Dave. I really appreciate the info. There is a tag on the cast body part that reads AUX 1307. Didn't know what it meant since I was already locked into the AUB 662 bit, so I've got a bit of a 'duh' moment. I'll conduct the tests as soon as I finish my honey-do list. I can already tell that the flexible fuel lines at the back will likely need replacing. Their ends are deteriorating and they are coated with dirt, grease, and oil. I suspect they've been on there a long time. I think I'm also going to take a look at the vent lines and the metal/flexible lines to fuel evaporator can in the trunk. So far, I haven't picked up on any abnormal fuel smells, but I'd rather nip things in the bud. Mission creep y'know...



AmishIndy Avatar
Seth Jones
Wheaton, IL, USA   usa
1971 MG Midget MkIII "Guenevire"
2007 Mazda 3 "Porco Rosso"
Nice articles! I added a link to your site from the fuel system page in my tech index. Thanks for the tip.

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Glen Phillips
DFW, TX, USA   usa
1972 MG Midget "Annabelle"
1976 MG MGB "Guinness"
1977 MG Midget "Widget"
Conducted some tests and it turned out the flexible fuel lines had lost their integrity - expecially the tank to pump line. The lines were replaced, everything hooked back up, and the car fired right up after a few seconds of pumping fuel to the carb.

Still have to replace the vent lines. They were jury rigged by a PO along with the removal of the evap tank. I did find one of the evap hose fittings - a metal tube coming up out of the tank and secured by a lock nut - has a hole in it. There's nothing in the Moss catalog about the fitting, either in the fuel system or emissions pages. Any idea on where to get one or should I simply try to plug the hole?

Pics show newly installed pump and lines and the holed fitting.



fuel_pump4.jpg    89 KB

fuel_fitting.jpg    66.8 KB
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