1995 Evinrude 48 started revving and then wouldn't quit.

[wish2fish]

I started my 1995 Evinrude for the first time. Started great and ran at idle without a problem. I added a can of seafoam to the fuel and shortly after I did notice more smoke coming from the exhaust. I noticed the motor didn't seem to be getting hot so I put in neutral and advanced the throttle. Shortly after doing that the motor started revving excessively. I turned the key off and the motor kept running. I then pulled the safety key and the motor kept running. I then disconnected the fuel line and eventually the motor died.

What could have happened that caused this motor to do this?

 

[hystat]

the spark plugs or carbon chunks or both get hot enough to glow and act like glow plugs igniting the fuel air mix continuously. This is common with 2 strokes and is one of the reasons they recommend not revving up an outboard in N on the muffs.

The 40/48/50 Johnsons and Evinrudes are known to run away easily when there is no exhaust back pressure. They have such a lightweight rotating mass.... the flywheel doesn't weigh much.
Idle it only on muffs.

My 40 has never done it and I think part of the reason is just the heavy stainless prop I have... I'm really careful not to rev it out of the water.