And you will not hear one. No matter how good your hearing is.
The electrothermal valve in the Primestart device does not get its electrical power from the key switch.
It's the innerweb! Amazing place.
Got a problem that a Yamaha Master Mechanic cannot solve? Someone on the innerweb knows exactly what part number needs to be replaced.
Hell, folks got solutions even when there are no problems.
First sentence says "I have no spark".
Second sentence says "Ran motor for 15-20 minutes...".
I am confused. How was the motor able to run for any time at all without spark?
Since the fuel enrichment device on the OP's model is not automatic, I withdraw my incorrect comment about it being a Primestart device.
Too many differences with Yams to try and keep tabs on them all.