How many filters do you have? Everywhere you have rubber hoses and clamps is a potential source of leaks and air introduction to the system.
Simplify your fuel delivery system and get rid of all but one filter. Try to use steel connections wherever possible instead of rubber hoses clamped to metal tubes.
As stated above, I had similar issues with an old tank and a fuel line that had several "repairs" in it (damaged sections cut out and replaced with rubber hose or a filter).
Anyway, the carburetor will normally have a little screen in the inlet port or a screw in metal filter where the pump to carb line comes in.
