Well... I'll tell you this....... if you were trying to hold the spark plug against the engine and pedal it and you got a BIG SHOCK UP YOUR ARM...... then you need a NEW SPARK PLUG !!!..... the shock up your arm is your tip that your IGNITION SYSTEM IS GOOD
When I'm working on a strange (to me) bike .... sometimes I will let myself get shocked ON PURPOSE.... and when it happens I smile because then I know the ignition is good to go !!........ if it's got enough to jolt the crap out of you it's got enough to spark a GOOD plug.
The only other cause is if the spark plug tip (in the wire) is not contacting the wire... or if the wire is pulled part way out of the spark plug cap (and you got jolted through the wire)
Spark plugs in 2-strokes are very tempermental..... and once they get fouled they will make you think that every thing else is wrong..... cause the plug can still look pretty good...... and mopeds have weak ignition systems that won't fire a dirty plug.