I have a GMS 40 and GMS 47. I think they are both great and would purchase another if needed. The 47 has tons of power. Other pilots are always asking what I run after they see it go. It idles very low and and has lots of thrust when wide open. Both the 40 and 47 have the same block. The 47 has a larger bore. I did have one problem when I purchased the 47. My 40 was running great but I just couldn't keep the 47 running more than a few seconds over 1/4 throttle. One of the guys at my field said it seems like an air leak. Upon further investigation I noticed on my 40 a small red washer (gasket) used on the carb barrel set screw. The washer was missing on my 47. I went home, cut a washer from a sheet of gasket material I had, replaced the screw, and fired up the engine. It worked right away and has never had an issue since. This is no fault on design, someone just forgot to put the gasket on before shipping. So, I'd say check that out when you get yours and have fun. I ordered from mecoa.com. Send them an old engine with no missing parts and they give you $20 off.

One other note, seems like my 47 is kinda quiet compared to other 40 size engines. The pipe is a bit larger than most.

-Rocko