I was on the water running about 3'4 throttle when all of a sudden I get this bad vibration in the motor and the speed dropped. Stopped & checked prop nothing tangled in it. Started back up and will idle to about 1500-200 rpm then the vibrating starts again. Got it back to the dock put one new plug ( all I had) and 2 older ones but still the same. I checked the prop and turned it by hand but it did not look like it was bent or wobbling. Idles fine until you give it some throttle then the motor wants to jerk back and forth, slow it down and it's good and this is with it in neutral . I haven't tried starting it since I got it back in to the dock. HELP PLEASE!