Bought a 2000 Johnson 50 hp outboard one year ago. Just attached it to my boat and started it up. Motor idled and ran well for a few seconds, then took off on it's own up to a high RPM even with the throttle at idle. Motor didn't shut down when I took the key out, so I pulled both spark plug wires. It continued to run despite having no spark. I disconnected the fuel line which finally stopped it after about a minute.
What are some possible causes of this behavior?
