The L-Jetronic and Hotwire fuel filter is mounted normally in the fuel line just upstream of the pump, i.e. the fuel flows through the filter before it flows through the pump. (SADLY, THIS IS NOT THE CASE WITH MORGANS). Ideally, a filter is needed before the pump not only to make sure that the pump gets clean fuel but because a filter on the pressure side can be dangerous. If the filter were to become clogged and fuel flow was significantly restricted, theoretically fuel pressure could build to dangerous levels and rupture fuel lines, causing gas leaks and possible fire hazards. In practice, this probably wouldn't happen as the pressure limiter in the fuel pump would prevent it, but engineers normally don't like to tempt fate and it's considered bad practice to put a fuel filter on the pressure side of the system. For this reason, it is even more important to change a Morgan filter frequently.
The filter is a somewhat large rectangular plastic box with a filter element designed to catch even very small particles. There is a paper filter element and immediately after that is a strainer. Charles O. Probst, in his Bosch fuel injection book, mentions that the paper filter has a medium pore size of 10 micrometers.
The filters have to be replaced every so often. I change mine every 10-15k miles, You can also know when you have to replace it by how the car starts jerking at high rpm, meaning fuel starvation due to a clogged filter. Of course, other things can cause those symptoms, but a clogged filter is always a possibility.
Fuel Pump Watchpoint
Owners of Morgans using the Hotwire and L-Jetronic fuel systems (Plus 8s and Plus 4s from the mid-1980s top the late 1990s) must remember never to run the fuel pump dry. Try not to run out of gas and please don't "bench test" fuel pumps. It is the fuel that cools and lubricates the pump; if they are run dry, they will overheat and become damaged very quickly.
Even running low on fuel may cause accelerated pump wear, since the pickup tube can occasionally suck air.