did you leave the fuel valve open overnight? Any leaks might drain into the crankcase.. the crankcase should be dry inside.
If the plug is wet it is fouling. If you changed nothing overnight, i'd suspect fuel in the crankcase first. This will foul the plug.
take the plug out and crank/pedal the engine for a while.. This should evacuate any fuel in the crankcase... then use a clean sparkplug and try starting it.
Test for fuel delivery by spraying Starter Fluid into the air intake. If it starts, chances are you do have a carb problem.