Kick starting

[JulianS]

High tensile cotters are available. I fitted one to my A10 years ago. Try an internet search if you want one.

[Tigerfeet]

My C15 chewed through two or three cotter pins. They would last until it kicked back. One kick back and they were done.

I eventually got a 'shallow' one from this chap https://www.ebay.co.uk/itm/204996210483  and have had no further trouble. (It has withstood several kick backs.)

The kickbacks have also been 'cured'. My C15 either wants tickling, or full choke when cold. But not both - both will always be rewarded with a kickback!

[Steve.S]

 If your kickstarter sticks down and then snaps back with a bang and stops the engine, this doesn't sound like the spring is returning the pedal. It sounds like there is something wrong inside the gearbox, perhaps the quadrant teeth are jamming up?
I think the reason no one has mentioned the notch, is because no one has ever experienced a notch before. This notch ties in with a possible gearbox problem and perhaps your broken (loose?) cotter pin? Who knows?
Kicking back is usually associated with over advanced ignition timing, but I seem to gather your engine is firing after TDC? On full advance, the points should just start to open when the piston is about 1/4" before top dead centre on the compression stroke.
Bearing in mind most engines will need a slightly different technique, I don't think it's necessary to position the piston after TDC, as on a vintage BSA with a valve lifter.
Just get the piston up to compression (so there's some resistance to your kick) and give it a good kick or three. If everything is as it should be, it will start. Ignore the ammeter, just concentrate on giving it a good hard kick.