I am interested in this topic, and would like to see the discussion grow and stay alive.

Here is my issue: I am thinking of scratch building a Goldberg Ultimate biplane. I have considered powering it with a DLE-20 gasoline engine, as that has been done before. However, that engine seems to be a good bit more than this plane needs, which flies great on a 4-cycle 120 glow engine. I would have to make a taller landing gear to accommodate the larger prop that would get the most out of the DLE. Plus, that engine is quite loud, and requires either an expensive aftermarket quiet(er) muffler, or a DIY one.

In summary, I would love to see a 15-18cc (guessing on the displacement) gasoline engine that swings a 14-15" prop and has very comparable power and weight (or lighter) than a 120 4-cycle. In other words, something like a slightly smaller version of a DLE-20.

Do you think an existing model glow engine could be converted to accomplish this, or perhaps an existing 2-cycle gasoline engine from some piece of power equipment?