do you have a long pressure line? try shortening it. the problem probably got better when you removed the filter because you removed some volume from the pressure line.

if the engine does not create enough vacuum on it's own to draw fuel into the the carb with a long pressure line, you can help it by shortening the line- adding pressure in the tank. with a new engine the line could be very long, but as the engine starts to lose seal a long pressure line will run lean.