Diesel heads have what is called a contra piston in them that is moved up or down with the screw thus changing the combustion chamber volume and therefore the compression pressure. On most European Diesels you just increase the compression pressure until the engine starts, let it warm up a few seconds, run it wide open and adjust the compression and the mixture for best running and fly. With the Davis Diesel conversions you use the same procedure except once the engine is set up you won't have to adjust it again unless there is a drastic change in the ambient temperature. With the Euro style Diesel you have to do the compression and mixture routine each time you start the engine.