Boomologist mentioned several good things to try....It sure sounds like it could be plugged pilot jet circuits in the carbs.
Were you able to actually remove both pilot jets from the carbs?
It takes a small, straight blade screwdriver with a very good, straight tip to get them out without boogering up the straight slot in the tiny brass jet.
Often just blasting carb cleaner, or compressed air through these jets while they are still installed in the carb is not enough to dislodge the "gunk" that has built up in the passage below the pilot jet.
Your fuel filter is probably fine.
I would remove those pilot jets and blast carb cleaner through the passage...if you use the little red nozzle on the can of carb cleaner, you can direct the spray right into that passage. When the passage is clear, you can actually see the spray coming out into the venturi of the carb....wear some eye protection while doing this...