HugMonster: You are very right. The flamewall of the fuel travels at about 50 meter/sek, and the speed increases a bit when the rpm goes up, and slow down a bit when rpm goes down. When switching off one ignitionplug, the flamewall now starts at the other ignitionplug, and since each cylinder have two ignition plugs, they can not be centered. Therefore the flamewall have a longer distance to travel, which means that the time the flame is pressent is longer, therefore leaving shorter time for the exhaust to cool before it reaches the gauge on the manifold = rise in egt. (There are other factors)