I've been trying to get my head around the way a Wico ignition system works on a Kirby-Tecumseh engine. The contact points spark in the open position. I have turned the crankshaft manually in a clockwise direction with the head removed. The points open fully just near the end of the compression stroke, to fire the spark plug and ignite the mixture. This is just as we would expect. But as I turn through the remaining strokes I notice the cam lobe also opens the points at the very end of the exhaust stroke. Clearly this is a "wasted spark" as there is nothing there to ignite.
My question is this. Is it unusual for a 4-stroke to have a "wasted spark"? I seem to have read somewhere that many 2-strokes do spark twice per cycle.
2 rotations of the crankshaft completes 1 full camshaft cycle comprising 4 piston strokes.
The Stens electronic ignition system that I fitted to the Wico coil now only fires the plug once every cycle, not twice. The computer chip evidently detects the wasted spark on the exhaust stroke and "turns it off".
