- Tue Jan 19, 2016 2:15 pm
#54355
Thack - the auto-decomp does kill the motor if the idle speed is lowered enough, do try it. You hear it cut in and the motor dies. You cannot kick it fast enough to get to 350rpm on the cam shaft (700rpm crank). As soon as it fires up it takes it straight over 700rpm. I suspect the ticking noise we hear first of all is the auto-decomp partially closed, the exhaust valve held open a little but not enough to kill the engine. Then it goes 'click' and the motor speeds up and settles down. Holding the exhaust valve open has much the same effect as a manual decompressor valve. But when the rpm drops below the necessary speed, the auto-decomp opens the valve on its full extra lift.