SpaceClam,

By the way, a smaller carb throat diameter helps idle and fuel draw, not hurts it. As Downunder said, most modern 2strokes have carbs that are much bigger than they used to be to try to get big power numbers, but they do that at expense of idle.

Losing a muffler in flight will of course cause poor idle. But it's entirely because of the loss of muffler pressure to the tank. If you set up the low speed mixture to be correct with out the muffler pressure, and allow for good fuel draw, you'll find that the idle will go right back to being just fine. The only valid test is to run an engine with muffler but with out the vent line attached and then run it with out the muffler, and see if the idle is affected. As downunder said, backpressure is never good (except tuned pipes)