The right pipe runs to the cylinder that points at the front wheel - the spark plug you removed. It may have been getting warm through conduction of heat from the other cylinder.

Remove that forward plug again, and plug the lead back onto it. Rest the metal portion against the metal of the engine, and have someone crank over the enigne (with ignition on and kill switch set to run) while you watch for a spark.

Come back and tell us what you found.
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