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MG MGB Technical - Fuel Filter

I am installing a new SU fuel pump in my recently acquired 74.5 BGT and was thinking of installing a fuel filter in front of (on the intake side) the pump. My thought is to keep any junk in the tank from going through the new pump. Will the the pump pull through ok or cause any problems?
Thanks
Scott Shirk

Hi Scott

Best after the pump.

The pump is electrically powered on the intake stroke, and delivery is by spring pressure on the outlet stroke.

If an upstream filter is fitted, and then blocks, the pump will remain on a power on position with overheating and possible failure to follow.

Down stream, this dosn't matter.

The valves are big enough to swallow and spit out fairly large bits of crud.

Cheers
ian F

Ian Fraser

Ian is absolutely correct. A filter that gets clogged on the inlet side to the pump will cause the pump to stall in a current on condition and if the power is left on for any length of time, it will burn out the internal swamping resistor (this resistor consists of very fine resistance wire wrapped around a card inside the coil housing and is very vulnerable to over heating). Once the resistor is burned out, half of the arc suppression circuit is gone and the points will burn rapidly. worse, since the damaged resistor can't be seen, new points will likely be installed and they will, in turn burn out prematurly, resulting in the owner cursing anything preffaced with SU. Worse still is the all electronic pumps in that in addition to the swamping resistor burning out, the circuit board will be damaged from over heating. Even if the circuit board survives, I was told by the all electronic pump expert at Brulen Fuel Systems that the all electronic pumps will not work at all if the swamping resistor is burned out. Bottom line, do yourself a favor and install the filter in the outlet side of the pump. Cheers - Dave
David DuBois

Scott- What Ian and Davis are telling you is true. However, there is a way that you can install the fuel filter between the fuel tank and the fuel pump: Have the fuel tank purged of all rust bt rinsing with phosporic acid (never hydrocloric acid), then coated internally.
Steve S.

What Steve S said. Of course, after doing that, you won't need a filter. I would recommend doing that even with a new tank. I installed a new tank about 6 or 7 years ago and am already seeing signs of rust because I didn't coat the inside of the tank. Dave
David DuBois

When I pulled the OE tank on my 68 GT, it had a nylon mesh filter on the end of the pickup tube. Apparently, not every tank had one from what folks have said here and elsewhere. The replacement tank I purchased about 12 yrs ago did NOT have such a filter nor the internal baffles of the OE one. A cheap tank? I didn't think so, but it was what was available at the time from a respected vendor.

It would be nice to know if the new ones have such filters or not. Sloshing the tank as Steve S. suggests is truly the best way we have today of preventing muck from generating within a rusty tank, but I have been made aware of problems with that process if the tank has one of these nylon pick up filters. If the pickup has a filter, could clog if we don't blow back some low pressure air back down the pickup to clear it before the liner hardens.

Another option expressed here a few times is that the late model fuel level gauge sending unit also combines the pickup tube and using a later tank and sending unit would probably avoid any such situation and allow you to coat the inside of the tank with no problems.

Correct me if I am wrong, but these are considerations some folks have had to deal with, but that may not be true any longer.
Bob Muenchausen

I use one "upstream" as Ian put it. If you service it with some regularity it shouldn't be a problem. Also, the one I'm using is from an Audi, about the size of a pop can, lots of surface area to catch crud and still let fuel flow.

j
JohnB

This thread was discussed between 05/03/2006 and 06/03/2006

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