OK, A friend of mine got tired of trying to fly this 150. We have about 3 hrs running time on it and it is still very tempermental. Will not stay adjusted correctly through an entire flight. I remember a while back someone was modifying this engine with a head shim that was improving characteristics a great deal. Does anyone remember who this was and are they still doing it? Thanks for any info.

The very early 150's had more compression than the later ones. But they generally ran OK if you didn't use 30% nitro fuel in them.

These engines will either have an "A" or else nothing stamped on top of the right mounting lug. Engines with letters farther down the alphabet stamped on the right lug are not the high compression ones.

You problem sounds more like a air leak or fuel problem and not anything resulting from the high compression. The high compression engines gave more trouble when you were trying to start them. They would back fire and throw the prop on acceleration too.

Good luck,

Jim