I have just read this post as I too have had simular problems with my GMS 47. I had a very frustrating time with mine this summer when I mounted it in my See Bee 40 size pattern plane. I had run the GMS in my trainer before and It seemed okay, but once I installed it on my See Bee I would always lean out in arobatic flight and dead stick. I also had a MDS 40 so I swapped it out with the GMS and it would do the same thing as the GMS so I naturally thought it was somthing with the installation. But I could not find any problems with the fuel system. At our annual KWFD scale rally Flite Craft had a great deal on Super Tigre engines so I bought a G-51 and put it in the SeeBee and it has performed great right from the start.
I did check under the inlet nipple on my carb and the hole does not line up on mine, but by blowing air through it I would say it doesn't seem to be affecting flow much but I will rill it out anyway, just incase I need to use this motor in the future.
PS. I ended up putting the MDS 40 with the GMS old style muffler on my trainer with floats
and it has crazy power! This plane is at my cottage and I did not have my tack but it absolutly screamed with that pipe.