Hmmm? This sounds familiar! Here is what I had to do to get mine to run right AND most of the time.
1. I am running a TT Pro .46 muffler WITH the baffle in place
2. Disassemble all the nipples and fittings on the engine fuel system and drill
them out to make them larger and to unblock them. Clean everything out carefully.
Do not drill out the needle valve hole!!!
3. If/when I buy another one, I will run 2 gallons of fuel thru it before I try to fly it.
This thing blows black spooge out the exhaust but shows no adverse wear. It just
gets better.
4. Here is the big secret. You will have to run it way rich on the ground. Peak it out and
RICHEN it to loose at least 1,000 rpm. The low speed needle should be about 2 1/2
turns out.
5. My engine is real sensitive to weather changes, even on the same day!
This is a cranky engine and still will quit once in a while, but with an 11x4 MA prop and
10% fuel it will snatch a 5 pound airplane around pretty sporty!
If you are just starting to fly and looking for stick time, put the GMS away for now
and get a Thunder Tiger or an OS.