Spark timing is off. Check the points gap and the plug gap. Also ensure that the plug is the right one for the machine, according to the machine manual.
sheared flywheel key. youtube has vids... type in mower cord backfires & you'll see instructions on how to fix it.
generally the alternator sits under the flywheel
sounds like the clutch switch neeeds replacing or cleaning.
hurt no, if you pulled your cord and it jerked your arm and hurt you have a shear fly wheel key.
On most lawn mowers the coil and the fly wheel are located under the recoil housing or engine shroud.
you have to remove the flywheel with a flywheel puller or maybe knocking it off with small hammer blows.
Replace the keyway under the flywheel, change the camshaft timing.
You should be able to turn the starter with little effort when it is not engaged with the flywheel.
A gas lawn mower is a lawn mower which is powered by gasoline.
Probably a rusty flywheel and coil contacts. Take cover off and sand them.
Your flywheel key might be sheared
check the flywheel key. it sounds like it has sheared and will need to be replaced