I assume that the main filter is the one on the engine and the primary one is a Racor or other like it. Generally the engine filter is 2 micron and any filter before it is a 10 or 30. We daisy chain Racors. First Racor is smaller and 10 micron. After the first Racor is a much larger Racor with a 2 micron filter. From there it goes to the engine filters which are 2 micron and never need to be changed. If your first filter from the tank is 2 micron it's too small and will clog easily.

It's good that you don't have an electric pump as they can hide a problem. You might put one on a loop and use it only when necessary like when you need to bleed the system and then bypass it letting the engine use only the mechanical to keep the flow. If you ever have a small air leak you can put the electric back on line and pressurise the fuel system to keep going until you fix it.