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Kicking back and/or backfiring is most often a shared flywheel key throwing the egine out of time, so I would start by inspecting the key. Even a slight shear just enough to feel with your thumbnail is enough to to do it.
You'll need to remove the engine shroud to gain access to the flywheel. If you don't have a strap wrench for holding the flywheel, take a length of clean cord like starter rope and place about 3' in the spark plug hole to function as a piston stop to keep the engine from turning. Leave enough hanging out for easy removal. Loosen and remove the flywheel nut (or bolt) and washer, then look at the slots in the crankshaft and the flywheel. They should be lined up exactly square with one another. If they are not, the soft flywheel key has sheared (it's supposed to under some circumstances to prevent damage to the engine) and will need to be replaced.
A puller is the best method, but a way to work around if you are very careful is to loosen the flywheel nut and then thread it so that about 1-2 threads of the nut are covering the threaded end of the crankshaft. You want the crankshaft threads fully protected. Then place a large screwdriver underneath the flywheel to use as a lever. Be very careful where you place it, since there's an alternator coil under the flywheel as well. Place the screwdriver end on a solid support under the flywheel such as a strengthening rib, then lever it up to put pressure on the bottom edge of the flywheel. Next take a mallet -- not a hard hammer -- and give the flywheel nut a sharp what while levering up with the large screwdriver. The whack combined with the leverage should release the flywheel from the crank. Then just remove the nut and take it off.
Here's some info that may also help:Extra Info
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