Nils, Good topic! The main reason I suspect is the much lower oil content. You are going from 16 to 18% oil way down to 6 to 8% oil. Also these engines are supplied with OS type F glow plugs which are the best. I do not run on-board glow in any of my engines. The other day I flew my 9-90 on my Robin Hood 99 7 times and never lost a cylinder!