I'd take the muffler off and start the engine without the muffler as it could be blocked (baffle could have come loose etc)

I usually just use a spark plug that runs in another mower that way I know it's not a spark plug problem as some plugs
spark on the outside but don't spark when installed this can be the same for a coil ,when I get a problem like this I like
to test the coil on another motor that runs as this rules out a spark problem.


Cheers
Max.