Mine doesn't idle well without the muffler, It isn't reliable at all without it. However, someengines won't even idle without it. a couple of times i have been at the basin when low and behold, off comes a muffler. They idle it down to land it, and their engine dies at about 1/4 throttle. a part of that non-reliability at idle without mufflers is indeed fuel draw. Because there is so little air coming through the carb, it does not suck enough fuel. However, with the big gas engines, They draw enough air that they will suck fuel at idle, But you will notice an increase in throttle transition by putting pressure in the tank or putting a pump on it.