This is the way you measure the timing duration: with a protractor circle scale made out of poster paper or cardboard place it loose on the prop hub, now place a paper clip on topof the cilinder an make a bend as to indicate on the scale the location of the degrees next while looking at the exhaust port, turn your crankshaft counter clockwise until the top of the piston is level with the top of the eaxhaust port, this will be your ZERO degrees point on your protractor, now keep turning the crankshaft counterclockwise until the piston goes down and then it starts going up again until it reaches the upper edge of the exhaust port this would be your total exhaust duration (the time that the exhaust port remains open, the longer it remains open the
more the exhaust gets out the cylinder