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MG MGB Technical - Best location for a pre fuel pump filter

What is the best location to add a pre fuel pump the gas tank outlet, midway between the tank and the pump or just before the pump?

I put mine at mid-point.

rick ingram

Same as Rick, and then another between the metal fuel line and the carbs, up on the firewall. Redundant, I know, but in my case, the OE metal fuel line had accumulated crud on its inside, which, apparently, the new type of gas we use today dissolved or ?? and was letting flakes of this crud pass on to the carbs. With both filters, I have had no junk in the lines, or the carbs.
Bob Muenchausen

I have a second filter in the same location that Bob describes.

I used a metal filter between the tank and the pump so that road junk has less of a chance of damaging the filter...and used a glass/high impact clear plastic filter with replaceable element under the bonnet. THis allows me to "see" whats going on with fuel delivery.

rick ingram

My recommendation would be to put it where it's easiest to get to for cleaning/replacement, and use one with a glass bowl so you can monitor it. I don't think the location makes any difference as to effectiveness, but if it's hard to get to, there may be a tendency to forget about it until it causes a problem.

Ask me how I know!
Dan Masters

How do you know, Dan?


(I still would not use a glass bowl between the tank and pump.)


I agree with Dan about location. The problem is that everyone's situation is different. If you replaced your metal fuel line, you probably won't have my problem with it. If you use an aftermarket pump with bypass capability, you can do as Rick and I have done. But David Dubois, our resident SU pump guru, is correct in stating that putting a fuel filter ahead of the SU pump is not a good idea.

It is not as simple sometimes as it sounds, to know what is the right thing to do. At the least, a filter, preferably transparent, ahead of the carbs is still a good idea.
Bob Muenchausen

As someone who repairs the pumps, my advice is to place the pre-filter either after the pump or in the trash! A filter between the tank and the pump can (and does at times) become so filled with fine rust particles that is stops the flow of fuel altogether. When this happens and if the ignition is left on while troubleshooting the loss of fuel, the pump is stalled in a current on condition, which then causes the swamping resistor that is internal in the coil, to burn out. Once the owner has found that the problem with fuel delivery is the filter and replaces it, the pump takes off and pumps fuel just fine and everybody is happy - for a short while. The swamping resistor is part of the arc suppression circuit for the points in the pump. When that resistor is burned out, while the pump appears to be working fine, the points are burning quite rapidly an soon the pump stops working. The owner bangs on the pump and probably makes it home, removes the pump, finds the points burned, orders a new set from Moss (or wherever) and replaces them, only to have the points burn out again in a short period of time, at which time said owner curses anything with SU proceeding the name, throws it out and puts in one of the little square, run all the time, make a lot of noise, Facet pumps and proceeds to bad mouth SU fuel pumps.

Easily 50% - 75% of the pumps that I get for restoration have the swamping resistor burned out. Nobody know that this happens to their pump because the resistor is inside the coil housing where it is hidden. I didn't know that such a thing existed prior to starting to press the coils out of the housing so I could bead blast the housing prior to painting them. Not even Burlen Fuel Systems knew why the resistors were burning out, only that they did and when they did on the all electronic pumps, the pump wouldn't work at all. You should have see their technician's eyes light up when I told him about the cause when I visited them a couple of years ago.

My recommendation is to not install a filter between the tank and the pump. Rather, it makes more sense to me to have the tank cleaned and sealed so that no rust forms in the first place (the fine rust particles will pass right through the pumps and be caught by a filter between the pump and the carbs). If you do install a filter between the tank and the pump, inspect it regularly and replace it when any debris starts to build up. Cheers - Dave
David DuBois

That's good advise, Dave...

I replaced the tanks with new ones on two of my MGs back in 1996, and have experienced no difficulties.

I replace the filters every other year.

How rapid do you feel the tanks may deteriorate such that the rust problem you describe will happen in the above scenario?


rick ingram

It depends on the brand of pump. When my SU pump died , I replaced it with a red Holley pump. Holley strongly recommend fitting a filter before & after their pump. Barrie E
Barrie Egerton

Rick - I put an unsealed tank in our MGB some 7 or 8 years ago and I am laready seeing signs of fine rust particles in the float bowls. Without a filter in front of the pump, the rust has to ge very bad before it will clog the pump, it just passes straight through the inlet filter that is in the pump, which is quite course. I did a pump for a friend and told him that he needed to check the tank because I found a lot of rust particles in the pump. He chose to ignore my warning and was back in about 6 months because the pump wasn't working. He stayed while I opened the pump and we found it packed so full of rust particles that it looked like the coffee holder from an expresso machine. His comment - "I guess I should have looked after the tank". So in answer to your question, thee tank has to be pretty bad, but I see a lot of pumps where the tank is obviously bad by the amount of rust that I find in the pumps.

Barrie - I should have preffaced 'pumps' with SU as that is the only type I deal with. If you are using Holley pump, then follow Holley's recommendation. I do know that Holley pumps are a centrifigual type of pump that runs at a rather high speed, so any rust particles that get into it, I assume, would do damage to the pump's seals. Also, being a centrifigal pump, it woulddn't stall out if there was a clog on the inlet side. Cheers - Dave
David DuBois

The pump I use is a Bendix and the reason I installed a filter ahead of this pump was to capture crap from the tank, even tho it was a new one, since it did not come with a fuel filter on the end of the pickup inside the tank, as the original tank did. A cheap tank? Who knows. It was what was available at the time.

In Idaho at the time I replaced the OE tank, gas could often be contaminated with crud right out of the pump (we have not always been as concerned with the niceties of maintaining tanks and gear at our stations as other places) and a filter seemed a prudent thing to do even with a new tank. If your tank has the filter on the pickup, you probably don't need the "prefilter" ahead of the pump in any case. But if your tank is like mine, perhaps it is not a bad thing, especially if you check it periodically as Rick does.
Bob Muenchausen

This thread was discussed between 15/01/2006 and 16/01/2006

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