Start with a clean plug if yours is black. Magnetron ignition is very reliable, either it works or it doesn't, but it doesn't have the energy to fire a fouled plug. As others have pointed out, you most likely have a clogged jet in the carb. Some later snowblowers, espescially entry level models, run at a fixed speed. Save your time on the flywheel key. If it was sheared, the engine will kick back and pull the rope out of your hand.

When you're done for the season, store the fuel system completely dry.