OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Tecumseh / Kirby Engines Do Phelon and Wico ignition have a "wasted spark"?

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".

Regardless of whether it is 4 stroke or 2 stroke if the ignition is driven directly off the crank it fires on every stroke, so 4 stroke runs wasted spark. Old 4 stroke points ignition motorcycle engines that drive the distributor or points of the cams (these are running at half engine revs) fire only on compression stroke so no wasted spark

A simple and succinct answer, for which I thank you.

After researching the topic some more, I see this same question pops up fairly regularly on forums all over the internet. Many of the replies waffle on and some claim that it is rare for 4-stroke engines to have a wasted spark. Well I guess they are right if we only consider "modern" 4-strokes which have electronic ignition. I suspect this is why there is so much confusion and people like myself keep asking questions about it.

The situation changes when you move from magneto ignition to coil ignition because in motorcycles as in one I have that I converted from magneto to electronic that has 2 firing positions on the electronic unit which is driven off the cam (so half engine revs) it fires in the correct position for both cylinders but then it is fitted with a single coil with twin plug leads, thus giving a wasted spark situation again. With this setup you can run either plug lead to either cylinder and it makes no difference. I just added this to muddy the waters a bit for you

And now I have a headache!

Now wouldn't that only apply to 180 opposed cylinders and not v-twins as v-twins fire number 2 fire 270 degrees after or 90 degrees before number one? Just asking as I don't work on motorcycles normally.

Yes AVB you are correct it only woks on 180 degree cranks mostly old Brittish stuff