[Corin Stormhands]

Make sure the connection is solid (not loose). The easiest way to test the spark plug is to just replace it with a new one. They're relatively inexpensive but might involve a trip to ~town~.

Beyond that...I googled this answer:

You can test the plug to see that it is functioning properly by grounding (touching) the hex portion of the plug to a bare metal part of the engine. Pull the rope or turn the key. If you see a blue spark jump across the gap in the plug, it is functioning properly. If not, a new plug may be the answer.

[HairOfTheDog]

Town? - I always get beat up when I go to town!