If starter fluid down the carb does not work, clean & dry the plug with some more starter fluid
Then give it a short shot down the plug hole and try again.
If it runs a few seconds till it burns off the starter fluid but you get nothing from fluid down the hole then you have a problem with the inlet valve.
Confirm this by pulling the rocker cover off and watch the valves moving , or most likely not moving as you turn the engine over by hand .
With your 3rd paw slip a pencil or BBQ skewer down the plug hole and try to relate the position of the piston with the position of the valves.
If the inlet opens when the piston is rising for instance then cam has skipped a few teeth