Setting the valve clearance out past max specs should raise the compression. Try doing this on the intake valve first.
but:
Did you install the $90 951-10309 replacement carb or the $15 clone carb?
You indicate it will start with starting fluid.
What if you use gasoline instead of the starting fluid as a primer?
If using gasoline does it act like it's flooded when it eventually starts?
(Does it have blue smoke or black smoke when it starts?
After the engine starts will it idle smooth if the carb throttle is manually held at low idle?
Some carbs have a big hole or holes in the choke plate. Trying blocking off the excess choke plate holes.
It appears the engine is very lean on gas for a start up. Make sure the choke plate is staying closed when cranking. Some push mowers have choke that only stay closed for few cranks of the pull rope. (manual lever type on the engine and no choke cable used)
AND
ALWAYS TRY A CORRECT type NEW spark plug gapped properly.
