you answered your own question about the duraplane.I have two Norvel's,they are so tempermental that I,m going to carry them to the lhs to sell,I don't plan on buying another Norvel.Most of my small engines are TT or OS,I like the OS best,I break them in by the instructions,then fly,maybe once or twice a year I change glow plugs,or twek the needle valve,have eight of the .15 to .25 engines,most are on combat or small scale planes.