RE: O.S. GF40 4st gas
I will agree, the DLE's are a bit simpler to deal with, I've got a whole fleet of them- 20cc, 30cc, 35ra, & 50cc, and they all run good.
The OS is not quite as easy to work with. I tend to break my engines in a little different than most, just a touch more oil and run the crap out of them, NO mercy!
I have yet to have a bad runner, EVER, seat the rings fast as possible with good cooling air.
I don't quite get the need to keep changing the plug for every day of running your engine, figure out the cause of fouling and fix it, be it oil ratio/rich mixture or whatever. I don't think I would be so quick to condemn the engine, OS tends to get there stuff right for the most part. Now my big Saito FG-57T twin gas, it has about 15 flights and is apart for bearings, and the cams run bone dry, I have to pump oil into the breather and tilt the plane on its nose to oil the cams. As a glow engine, they (Saito), are fine. Gas tend to run less oil. The OS is much better thought out in the lubrication regard.
Keep fooling with it, it will work, try a little less oil in the fuel, I run 30-1 Stihl hp ultra, and it seems to like it.
Mark.