I got my GMS 120 off the self the other day and thought I would give it a second chance.

I have it on a 66" Cap232, I had a YS 110 4 stroke on the plane spinning a 15/8 prop. The GMS is running on 20%nitro and an OS four stroke plug and is idling at 1800 to 2000 rpm. With a 16/8 prop I get 8200 rpm. The engine out performs an YS110, but you would expect it to. I would recommend a four stroke plug! and at least 10% nitro.

Tune up was fine, just using exhaust pressure for the tank. If money was no object I would buy a Moki 135 instead of a GMS120 or even an OS120 FS.

Not bad, but they are a cheap engine and YOU GET WAS YOU PAY FOR.