You pumped a lung full of rust filled water into the cylinder, the plug is now wet and likely covered in crap and quiet likely the carb is now full of crap again as well.
Drain and clean the fuel system, tank, petcock, carb. Put new fuel in.
Replace the plug with a new one (or if it's already new clean and dry it), try again.
It's also possible the decompressor is jammed. (unlikely but possible).