The best way to find a replacement engine (Magnum is no longer available) is to contact a dealer who sells the brand of engine you would like to use....
I highly doubt that you have a bent crankshaft on a 20333, unless you hit something so hand that this mower flew out of your hands. More than likely...
You are correct, it is a fuel issue. Suggestions, take the carb apart again and either soak it in carb cleaner overnight or take it to a repair shop...
After 34 yrs old teaching I now work part time for a dealer who has supported our program
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This is only my opinion, and many will say it ain't worth a darn, as I'm only a retired grease monkey instructor and not a professional mechanic. Use what I post at your own risk as you know teachers only know book knowledge.