Marine carbs are set up to run with VERY restrictive air cleaners.
Years ago I bought a carb and intake from a Marine 340 to use on my 360. It ran terribly. If I placed both hands over the carb while running and blocked off most of the air, it smoothed right out and ran great. I made a restricter plate out of the back piece of a Chevy starter with lots of holes drilled in it and used it until I could find a better carb.
Oh, to be 16 again........
Barry