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MG MGB Technical - Possible Fuel Pump Trouble

Okay, I did my requisite searches and found nothing addressing my situation, so I figured I would bring this before the group to see what I could find. I got my 73 GT (71 engine) started for the first time in 6 months (well I have only had it for a couple weeks, the previous owner let it sit for 6 months). I repaired a small leak around the fuel filter (I believe this was added aftermarket) and the car fired up great, ran for about 10 minutes or so with the idle a bit high (1500). She ran until she sputtered and came to a halt acting like she was out of gas. So I went to the station near my house and picked up a 5 gallon can of gas and brought home. Filled the tank, started her right back up and she ran for about another 5 minutes before she sputtered and cut off again.
This time though, when I turned the key off and cycled it back on, I did not hear the fuel pump making any noise like it had the previous times I ran it. The previous owner said he replaced the original pump with a new SU (which is problematic from what I read). So here are my questions:
1) Is there a good way to test if my fuel pump has pooped out on me?

2) What is the line pressure and normal gph flow-rate for our fuel system (couldn't find this in my manuals or on the boards, only that the minimum flow is between 10-18 gph)?

3) If I purchased an aftermarket fuel pump and racing fuel cell, is there anything I should be watching out for?

Any info and suggestions would be greatly appreciated.
D. T. Barnes

Remove the fule line at the carbs and put end in a can and turn on the key. You should get around a quart in a minute. fuel pressure is roughly 2 to 4 psi. If you use an aftermarket pump you will need to install a fuel pressure regulator as the pressure developed is too high and will flood the float bowls.
John H

John - Thanks, we tried the fuel line trick you suggest and got nothing. Thanks for the info on the 2-4 psi setting for the pressure regulator, the one I was looking at came with a 5-18 (I want to be able to use this same pump/setup for the V8 when I put it in). Will have to modify my search criteria, thanks. Can anyone verify the 2-4 psi fuel line pressure, because the information I find is going to dictate a purchase here very soon?
D. T. Barnes

5-14 psi regulator, sorry for the incorrect info.
D. T. Barnes

Hi.

You might like to try running it (carefully) with the fuel filler cap removed, to check that the tank breather isn't blocked.

Don
Don

A quart per minute is optomistic by about a factor of 2. The best a AUF 300/AZX 1300 series SU fuel pump will do is around 2 pints per minute and the pressure is 2.7 psi or 3.8 psi, depending on the particular modle within the series.

DT - You can access my fuel delivery troubleshooting guide at: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
which may help you isolate your problem. The symptoms that you describe, leads me to agree with the concluson that Don apparently came to, that is your tank venting system is clogged up and causing a vacuum to be drawn on the fuel tank as fuel is pumped out of it. In the case of the 73 MGB, the venting of the tank is through the charcoal canister in the engine compartment via a line through the vapor seperator located on the right side of the boot area. The line from the charcoal canister to the vapor seperator has a union along it's length that often times rusts shut, thus blocking the vent. Good luck - Dave
David DuBois

Sitting is the curse of any MG. The miracle of the SU fuel pump is that you can "rap" it gently from underneath the car near the passenger rear wheel and it will take off (most of the time). It's been many years since I had an MG full time (just bought an LE a year ago), but I raced SCCA and drove MGAs, MGBs and MGCs for years. The aftermarket units back then usually lacked the longevity of the SU pump (failed in about 90 days) and often lacked the necessary fuel volume to feed the HS-4s that you are probably running. Some of the SU pumps were "screened" on the inlet and outlet, so check for a bird's nest. SU pumps can be refitted with a new point set (see Moss or Victoria British), but that usually doesn't last forever. Note the "air" line that comes out of the fuel pump and if it's clear. The point area gets warm and needs to breath. Some of the gurus here may have different suggestions, but I've never found a better pump than the SU. SU used to have a very good warranty. I don't know if you have the receipt or not, but worth looking at.
Rick Penland

Don - in going back over my manuals and talking with some buddies, we arrived at that same conclusion, that is our next step in looking for what is happening.

David - so running an extremely low pressure like 4 psi or less is probably more realistic? Got it.

Rick - I do have the HS-4's and your are correct about the fuel volume. My idea was to purchase a Holley pump (110 gph) and use a regulator to control the flow to the correct pressure for the HS carbs. Then when I got my V8 built back up, I could use the Holley still and just up the line pressure to match. But that was just an off the cuff, real quick gameplan. Any suggestions?
D. T. Barnes

DT - If memory serves me correctly, the AZX 1300 series SU pump is also used on the V8 cars, since they still use SU carburetors. I higher volumn SU pump can be purchased from Burlen Fuel Systems (maker of all things SU) at: http://www.burlen.co.uk/. The higher volumn pumps are the LCS pumps (AUA 152 orAUA 157) or the double ended pumps such as the AZX 1400 series. As Rick stated, the AZX 1300 and 1400 series pumps have a screen on the inlet side to filter out large rocks and small birds. The LCS pumps have much finer filter screen in them. With today's fuels, a filter is not all that necessary as long as the fuel tank doesn't have larger amounts of rust inside it.

The reason that a SU pump will require a gentle tap to get it going after a long layup period is that the contacts on the points develop a film over them that is burned off in normal use. In layup periods, this film builds up and insulates the contacts one from the other. If the car is going to be stored for long periods or over the winter, is is a good idea to get either Burlen Fuel System's all electronic pumps or have me modify your present pump for solid state operation. Either route gets you a pump that doesn't have the points in it to film over.

Since Rick's experience with aftermarket pumps, a lot of them have improved to the point that I advocate installing one inline with the SU pump and then wiring the pumps through a switch, so either one can be selected. That way, in case of a pump failure, you can still get home without crawling under the car to swap out pumps (see my article on back up pumps at: http://www.custompistols.com/cars/dave/BackUpFuelPump.htm
Good luck - Dave
David DuBois

David - Thanks for the reply, I had looked at that route as well. I am planning on running a Ford 302, and putting in a different fuel tank completely (an aftermarket larger tank). I was trying to find an aftermarket fuel pump and line pressure that I could turn down to run with the stock motor and then turn up to run with the 5.0L when the time comes. I think I have found a solution, based on the line pressures of the stock engine being in the 2-4 psi range. I also need to do some more homework on the charcoal/evaporative loss cannister you refer to in a previous post.
D. T. Barnes

SUs are very reliable, not problematic. However I've had more problems with the new-fangled electronic style and gone back to the points type.

If the pump clicked and the engine ran as you described when first switching on the ignition then oxydised points are unlikely to be the problem. When switching the ignition off then on a short time later is it quite normal not to hear the pump click as the sytem is already pressurised. Conversely when you are out of fuel the pump clicks ten to the dozen.

If you didn't get any clicks or fuel with a pipe disconnected from the carb then there are a number of electrical and mechanical things that could be wrong, like a bad connection in the electrical supply or a blockage in a pipe, as well as something inside the pump.

V8's used the same pump as 4-cylinder cars (not just because they also used SU carbs) and at one pint per minute thety are capable of emptying the tank in a little over an hour - that is some performance/fuel consumption!
Paul Hunt 2

Paul - Thanks for the information. I was not trying to say anything bad about the SU design or functionality, I had just seen it posted that sometimes the SU pumps could be problematic, someone elses words not mine. I was thoroughly impressed when the car started right up after six months of sitting in someones garage. I am thingking I will first go through and check all of the mechanical aspects (tubes clogged, evaporator clogged, tank vent etc.) because I checked the voltages and the pump is getting the juice it needs to run, it just isn't pumping. I just haven't had the time to jack her up and crawl under to disconnect lines and check. I would absolutely love to keep the SU pump on the car, just need to trouble shoot.
D. T. Barnes

Did you check for 12v against a chassis ground or against the black ground wire on the pump? It should always be the latter, the pump ground (which terminates under a bolt head in the boot with fuel pump and reversing light wires) can also be a problem.
Paul Hunt 2

All good advice here - it sounds as 'tho the engine runs on the fuel in the carb bowl and then stops until it fills up again - my money is on a blockage - vent or filter or even a comstrained fuel line.

those thinking of pressure reduction valves might want to bear in mind that they can also fail - with catastrophic results - the FI system wants around 40 psi - the SUs want two and a half - in both cases the volume requirement is similar.
RMW

Paul - I checked against a chassis groudn but I couldn't get my multimeter lead to the pump gound with it mounted. Will try when I bring it out, if the clogs arent the problem.

RMW - Thanks for the info. I will let everyone know what comes of it. Gonna be a bit thought because of work schedule...
D. T. Barnes

This thread was discussed between 05/12/2005 and 08/12/2005

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