For the original SU fuel pump it is recommended not to put any filter in line before the pump, as any restriction on the inlet side may stop the pump from sucking in fuel. For many aftermarket fuel pumps it is recommended to use a filter before the pump, and many of the aftermarket pumps even have a small filter included in the box. Some even say it will void the warranty if you don't have a filter before the pump.

If you suspect trash in the fuel system, for an expedient fix you can install a clear plastic filter in the hose before the carburetor. This requires cutting the hose, which may not be desirable if you have a braided steel hose covering or if you just bought a new hose with the proper end fittings. If you have an old hose you can cut away the crimp ferrules at the ends of the hose to remove the end fittings with hose barbs, then install new hose with band clamps using the original end fittings. With a clear filter in line you can keep an eye on it. If it gets clogged up in short time you will need to clean the tank.

If you want to avoid a clogged fuel filter, remove it from the car.

MGA did not originally have a fuel filter, and should not need one. There is a screen in the fuel pump inlet, and also screens in the float chamber inlets. These screens should catch any debris large enough to clog a float valve or a main jet. Otherwise SU Carburetors are very tolerant of a substantial amount of dirt in the fuel system. Anything small enough to pass through the screens will also flow right through the carburetor without problem.

If you have enough junk in the fuel tank to clog a screen, then you need to clean the fuel tank. Starting with a clean tank and clean fuel, if you drive the car regularly the fuel flow will constantly cleans the whole fuel system, and you will never have a clogged filter.

If you don't drive the car much, or store the car for several months with half a tank of fuel, then it can eventually get rust in the tank. Either of these habits is a case of bad maintenance ($.02). If you insist on doing this, then a fuel filter may be a temporary alternative to periodically cleaning the tank. Never install a filter between the tank and an SU fuel pump (install it downstream from the pump). Some aftermarket pumps recommend a filter before the pump.

If you install a filter that will catch debris smaller than the screen openings, then you can throw out the screens downstream from the filter (or leave them in place with no harm). The filter will then catch smaller debris that would otherwise not affect the carburetors. This increases maintenance, requiring more frequent filter service (cleaning or replacement). Larger filter requires less frequent service. It also clogs up more gradually, so when it first gives signs of problems (bad running at high speed) you have more running time at higher speed before it gets much worse (less likely to cause traffic problems, and more likely to get you home).

When your filter clogs up more frequently than you like to service it, then it's time to clean the tank. Certain kinds of debris will clog up the works regardless of filter or no filter. Large enough junk in the tank can clog the entrance to the fuel pickup tube. Never use RTV sealant anywhere in the fuel system, as it can flake off inside to clog things up. Bare cork gaskets should seal the fuel sender unit. Thick paper gasket works for float covers or serviceable filters with no sealant required.