I have similar issues with my GMS-47. When it runs, it runs beautifully, but some days I have been unable to get it running at all.

What I finally seem to have found, is that the low speed needle valve has a mind of its own. Whenever I am at the point that it won't run, I look at the LSN and it is WAY too rich. I screw it back in to the factory setting (2mm? I think), and it goes right back to running great. I don't know why it is backing itself out, there is plenty of tension on the screw, but I do find that at the setting called for in the manual, the thing runs like a champ.

You may want to check your LSN valve, and lean it out a bit (or a lot).

Good luck


PS - The other problem I had with the engine was the muffler bolts kept coming loose. I ended up putting on longer bolts with nuts on the outside of the muffler, and used red silicone to seal up the flange as well as the muffler segments and pressure nipple.