I would also reccommend that you remove the carburetor and drain the water thats in it, even if theres just a tiny amount. The above ppl have a great ideas also . And could be almost anything. If you are not familliar with this type work, i personally would take it somewhere if i was unsure if what exactly to look for in this case..im not saying your not capable, im simply saying rather than chasing everything down, best of luck

You changed the spark plug and wire did u crack the engine over with the spark plug out? I would imagine your cylinder is full of water if you haven’t gotten the water out of the cylinder. It would have filled up through the carb/air intake also I would assume you have a fuse somewhere that could have blown

You say it won't crank. Do you mean the motor will not turn over or it will not start? If it will turn over then first check for spark. Pull the plug and ground it and make sure you have a good steady spark. Make sure there is no fuel around when you do this. If no spark then it is electrical. Cdi, coil etc. If you have spark give it a shot of starter fluid and it should hit. If it does then you have a fuel/air problem.

Sounds like electronic problem. I would go threw it little by little starting at the magneto
And you find the problem...
They sale used parts on eBay also google..
It could be many things... Good luck

Cdi box get wet ?