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MG MGA - Fuel Filters

The original A setup has some simple filters both in the fuel pump and also carbs, which are only gauze wire. While this does block out the lumpy bits, using old fuel tanks in our MGA's, we're bound to pick up smaller bits of "crud" that will get through, upset our fuel float needles and jets.
I don't particularly wish to stick something in the engine bay which wasn't original, like an inline shiny or cheap plastic fuel filter which technicaly is a good idea. Therefore I'm planning to stick a cheap plastiic one inline inbetween the tank and fuel pump, close to the fuel pump. Now for the big question. Does anyone know the thread size of the fuel pump pipe unions from the tank to the fuel pump?? I'm planning to use a screw fitment union to convert to 5/16" pipe to interface to a standard palstic inline filter. What have others done? Perhaps many of you may have cut the feeder pipe inline with the tank and pump to slide a fuel hose directly onto this and isert an inline filter. If so what is the diameter of the fuel pipe as what size fuel hose will fit, !/4" or 5/16"?

Many questions here, but the solution I'm looking for is a good technical solution and out of sight.

Martin
Martin Smyth

Martin,

I don't like putting paper filters in front of SU pumps, only after the pump. The pumps perform better against restrictions on the pressure side than against restrictions on the suction side.
Any particles that pass through the gauze wire filter are small enough not to affect the pump operation.

Mick
Mick Anderson

Hi Martin. I understand your dislike of fuel filters in the engine bay. When my MG carbs started flooding routinely because of dirt in the gas tank, I decided a fuel filter was the best solution. The fancy glass filter I got ended up in the engine compartment because I was afraid it would get broken if placed under the car. A tough plastic inline filter after the fuel pump, and under the car in an easy to change location might be the ticket. My inline filter coupled with grose jets cured my flooding problems completely. Cheers! GLenn
Glenn

I can't log on to get into the archives at the moment but I seem to recall a thread similar to this last year in which we were strongly advised by an SU expert not to put a filter before the MGA's pump.

But I may be wrong..... I will check later.

Steve
Steve Gyles

Martin,
I installed a metal inline filter just after the fuel
pump. You can tuck it up pretty well so that really nothing can hit it from under the car. I used metal in case any shock and vibration down there might crack a plastic one. I too didn't want to stick something in the engine compartment.

Ralph
Ralph

Steve - That was probably me expounding on filters on the inlet side of the SU fuel pumps. I advise against placing them in that position because if they clog to the point that the pump stalls, the pump will stall in a current on condition. When this happens, the internal swamping resistor (which is part of the arc suppression circuit, or in older pumps, the entire arc suppression circuit) will burn out, which in turn causes rapid burning of the points. Worse, any new points put int he pump will also suffer from a very limited life due to no arc suppression. Further, last summer, while in England and visiting Brulen Fuel Systems, their main all electronic pump expert told me that in the all electronic pumps won't work at all if the swamping resistor is burned out.

My advice has been to place any filters in the outlet side of the pump, between it and the carburetors as Martin and Glen suggest. I would further advise that if you are experiencing any debris in the fuel system, get the fuel tank cleaned and sealed against further rusting. Filters may keep some of the debris out of the float bowls, but don't cure the problem of a rusting tank, which will only get worse if not corrected. Cheers - Dave
David DuBois

Dave

Brilliant. I can almost remember your advice word for word now that you have repeated them! At 59 my brain is not totally dead - yet!

By the way, I used to live only 5 miles from Burlen Fuel Systems in Salisbury. But in those days I could not afford an old classic so I had no need of them.

Best Regards

Steve
Steve Gyles

Steve - We were staying with friends in Urchfont, just outside Devizes while in England, so were not far from Sasisbury and Burlen Fuel Systems. Beautiful countryside there in Whiltshire. It reminded me a lot of south western Washington state, with all the farmland. Cheers - Dave
David DuBois

David I am curious to understand your thinking? why would a blockage upstream of the pump have a different effect to a blockage downstream of the pump. In my small world both would restrict the pump equally. Also the closing of the carburretor needle valve would have the very same effect, wouldn't it?
Bob (robert)

I agree with Dave and I personally think instead of putting a band aid on in the form of a fuel filter, how about cleaning the tank. What is going to stop your aftermarket fuel filter from clogging up, and stopping you when you least expect.I hate to keep harping but after my frame up restoration 20 yrs ago car has not missed a beat,with the exception of a bad rotor.Clean and seal the tank,put on new lines,new pump, stay out of off brand gas stations and don't fill up when they are getting a fuel delivery. Gary
gary starr

Perhaps the difference lies in a pump full of fuel vs. an empty pump?
Joe Cook

Bob - It is not just my thinking, it is my observations of pumps on my test stand. While a blockage on either side of the pump will stall the pump, it is the condition of the points while the pump is stalled that is critical. A blockage on the outlet side of the pump is the same as the condition of a full float chamber that stops the pump after the diaphragm has been pulled all the way up. at this time the points open and allow the volute spring to push fuel out of the pump to the carburetors. I am sure that the designers of the pumps quickly realized that during this period of time, the pump needed to be in an "idle" state so that no current was flowing and generating heat. Conversely, if the blockage is on the inlet side it will cause the diaphragm to work against a vacuum while the points are closed and the solenoid is trying to pull the diaphragm up. Stalled in this position, the pump will continue to draw current and the coil will heat up to the point damage if the power is left on for a long enough time. I have noted in at least 50% of the pumps that I restorel, the internal swamping resistor in the coil housing is burned out, which reduces, or eliminates the arc suppression circuit, resulting in short life spans on any points installed.

Since my shop and test stand are in my basement garage and I use kerosene as a test fluid, I have gone so far as to hook up a thermal shut off for the power to the pump under test. This way I am assured, that if the pump fails in a current on condition while on the test stand and we are having dinner or, worse, asleep at night, we don't suddenly have a fire in the basement (that could definitely ruin ones restful night! Cheers - Dave
David DuBois

Thanks for the reply David, let me get my head round that for a day or two and hopefully I will be a little bit wiser.
Bob (robert)

This thread was discussed between 31/05/2005 and 02/06/2005

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This thread is from the archive. The Live MG MGA BBS is active now.