We have a 94 Yamaha Wave Blaster with an after market primer. Not often, but we have a situation that when the blaster is started, the engine will run at full throttle for about 30 seconds, without the throttle being squeezed and will continue after the key is pulled from the button. After 30 seconds, the blaster will die or the throttle will resume working. Both times the blaster was on the trailer in the yard and not on the lake. Any ideas where to start?