fx series are not abc, they are abn. Second of all, When you take the muffler off a 2 stroke, they will not idle well if they will idle at all. Without the backpressure, the pressure behind the piston just above the botom of the stroke will be much higher than it is on the top. That causes them to idle poorly. Haven't you seen those early rc two stroke motors? they have no muffler, but they have a mechanically operated valve at the exhaust. It is almost completely closed at and idle, and fully open at full throttle. I don't know why people are having that air bleed problem. this is not the first thread about these fx series having that problem, but i have never had it myself. However, fuel tubing, silicone glue, form-a-gasket, thread locker, teflon tape, and even epoxy would fix that problem.