ORIGINAL: Harry Lagman
If you buy a GMS 1.20, there's a better than even chance that it will run very rich in the mid range (1/4 to 3/4 throttle), especially in-flight, even if your low speed and high speed needles are adjusted correctly. It appears that at least some of these engines suffer a carb calibration problem in the mid range throttle zone.
I find that you MUST lean the low end more than you would normally, using standard tuning proceedures, on the 1.20 GMS and then richen the high end up a bit more than you would normally.
This cures the mid range transition problems once the engine is broken in.