[kip51035]

Some months ago I reported that my new, with several break in runs, GMS .40 was a real dog of an engine. I had a wandering mixture and seizing from over heating. It had eight or ten runs on it. I did three things:
1. I put an Enya .35 carb on it. inside diameter is .230
2. I put a .040" aluminum spacer under the head.
3. I added a little castor to the fuel so there is 20% oil.
I ran it today. I ran it at full song for ten minutes. On a 10X6 prop it turned 14,400, I backed it of to 14,100 and let it run the tank out, about ten minutes or so. Same note, nice stream of smoke right through to tank empty and when it quit the engine was not without compression like normal, it was not extra hot like normal. I think that these are good numbers and the fact that the mixture did not change was a bonus.

Kip

[Cougar429]

I got a GMS47, along with a 40FS, with an uncovered airframe I bought late spring. Both motors were very low time, but had obviously suffered from no after run treatment and the bearings were pooched.

From what I found online, the GMS engines suffered from air leaks at the base of the carb, which could explain all of your symptoms. ABC engines need to be run slightly rich to prevent overheating and damage/seizing of the piston and sleeve. It would also seem to be confirmed by the fact your new carb does not show the same characteristics.

Once I finished bead blasting the bits and the bearings arrived, upon assembly I installed a thicker O-Ring down in the bore and a thin one against the base of the carb body. This double sealed the carb and it has proven very effective. During testing that 47 has some serious yank with a 10/6 3-bladed prop! In fact, this post decided for me to head on down into the build room to bolt it to the front of my new plane.

[kip51035]

Before this the best run I had was nine minutes at full throttle, it got very hot and stopped with no compression. It did it three times. The throttle was wide open and once I set the needle I did not touch anything. A minutia leak at the base of the carb at full throttle would have no effect on the mixture. Change the "O" ring is not a cure all.

Kip