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MG TD TF 1500 - 54TF fuel pump siphon question

If I want to insert a fuel filter in the gas line where it runs along the frame will the fuel in the gas tank siphon out through the fuel pump when I cut the line to install the inline filter?? I guess another way to ask this is - do I have to drain the tank to install the filter?

Thanks... John

John - Since the fuel line comes out the bottom of the tank, there is no siphon involved - cut the line and fuel will drain out under gravity until the tank is empty. Your best bet is to install the filter between the pump and the carburetors. I say this for two reasons, one being the above, the other is that a filter on the inlet side of the pump can damage the pump is the filter becomes clogged - see the article, SU Fuel Pumps Facts and Myths in the SU Fuel Pump Articles section of my web site at: Cheers - Dave
David DuBois

Here's one I did earlier! You just cut the fuel line and the filter is a push-on fit with clips on the pipes.


A R Jones

I'm a little puzzled as to what value a filter after the pump would have. Seems to me that the filter in the pump itself would preclude the need for any filter further down stream. Help me out here Dave.
L E D LaVerne

Thanks AJ & Dave. Dave, your right, siphon was not the correct use of the word here. I want to put the filter in the line between the pump and carbs and my question should have been will the fuel 'drain through the pump' if I cut the line just before it turns to go up the firewall. Was thinking the pump might hold the fuel back unless it is running. Been having trouble with fuel overflow from the front carb. Had a bunch of crud in the float bowels. Changed the needle valves to gross jets and still have the problem on the front card which drains out if the car sits for a number of days. No leaks visible on the outside of the carb. Not sure what is going on. I did the inside of the gas tank with one of the kits you buy to seal it and have a new fuel pump. The crud looked like it had been there awhile so maybe it came from the old gas lines that I reused. Anyway, thought I would put a filter in-line just in case there is more crud. AJ's way looks like it might be easier so I might just cut the braided SS line I have going to the carbs and put a filter there.


I have a commercial mower that has a fuel filter prior to the pump. The carburetor needle and seat is quite tiny and it kept getting blocked. After the third time of cleaning it out the light finally came on and I figured out the pump itself was the source of the problem. Little specks of rubber were detaching from the diaphragm. I added a filter after the pump and voila, no more problem.

I left both filters in place. They are clear plastic and the one prior to the pump displays the junk it's caught such as the odd blade of grass that finds its way into the fill and the one after the pump displays the bits of pump it's catching.

The pump finally quit when the wires broke and I installed a spare. It will always have a filter.
J E Carroll

LaVerne - The OEM filters in the tank, pump and the carburetors are a relatively course screen, meant to stop rocks and small birds - they do not filter the very fine rust particles. The SU fuel pumps and carburetors are fairly immune to the very fine particles (no very small jet orifices), but people (particularly us Yanks, who are used to Holly carbs with their very tiny orifices) cringe anytime we see any kind of debris in the carburetor float bowls and immediately want to install a sub micron filter to keep that junk out of the carbs. There is no problem with that philosophy except that high efficiency filters sold today will clog fairly easily and if said filter is between the tank and the pump, causing the pump to stall in a current on condition, resulting in damage to the pump. This is the reason that I suggest that any high efficiency filter that is prone to clog with the very fine rust particles be installed after any SU fuel pump, where a stall will not damage the pump. To answer your specific question "I'm a little puzzled as to what value a filter after the pump would have.", probably very little, other than to make the person who feels the need for additional filtering feel like they are doing something to extend the life of the car. Personally, I have never added any kind of a filter to the fuel system in either our MGB or the TD and have never observed any negative effect. Cheers - Dave
David DuBois

John - Sorry, I didn't answer your question in my answer to LaVerne. Yes, the fuel will drain out through the pump because the cut you are making is below the level of the tank. Your best bet would be to pump (or siphon) the fuel from the tank into a couple of 5 gallon buckets before doing the work. Cheers - Dave
David DuBois

This thread was discussed on 12/12/2012

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