2-stroke engines run fine with out a muffler, in fact that was the way most of them used to be run.

It's true that a good muffler will increase power though tuning effect, though most stock mufflers actually reduce power by a few hundered RPM.

Fuel draw in the air in various attitudes is usually much better with pressure to the tank. But I wasn't talking about flying it that way, just a quick run up on the ground to check the RPM. Basically a test bench run. Fuel draw shouldn't be a problem if you locate the tank high enough. You could even use an external tank.

Either way, it's not a big deal. I suspect you will find exactly what you said you expect to find, that the engine is just plain old underpowered. Thanks for bothering to test it though, I'm sure curious to see what the result is.