Another possible source for high rev flame out is glow plug. Recently, I had a OS #8 plug replaced in my F20 that solved the problem with high revs flame out in the air. My theory is that the plug coil separates with heat expansion at high revs, and cause loss of glow. My motor was running slightly rich and still flames out at high revs until the plug was replaced. And it was not an old plug either.[:-]