88 Mariner 80HP couldn't shut it down. Even after pulling plug wires.

[Sinxb100]

You
88 mercury Mariner 80hp. Just got it and got it running. Ran it in driveway a few times and took it on water once but had a broken swivel bushing. Replaced today and ran it in driveway. The engine idle was high I did not adjust anything. The rpms kept rising so I hit the kill switch which was working fine then turned off key.. kept running at high rpm.. pulled all 3 spark plug wires kept running!! I have never seen such a thing. How can it run with plug wires off and why did it do it? I did put some seafoam in the tank btw

 

[jimmbo]

It is called Runaway. It has been mentioned many times as a Reason not to Rev an Engine in Neutral, especially on Muffs. Disconnecting the Fuel source is about it, hopefully the engine will survive that abuse

 

[Sinxb100]

I don't have throttle control on my main controls. It kept going higher on its own. That's why I was trying to shut it down.

Reason or solution?

 

[jimmbo]

I think you are going to have to do a complete Timing Check, and Synchronization of the Carbs and the carbs to Spark Timing.

Both carbs are supposed to be fully closed at Idle

 

[GA_Boater]

I don't have throttle control on my main controls. It kept going higher on its own. That's why I was trying to shut it down.

Reason or solution?

Reason - Primary, no load on the prop. Secondary - No controls.

Solution - Hook up the controls and don't rev it more than about 1500 RPM on nuffs.

 

[roscoe]

Google "2 stroke runaway" for more details.


Engine runaway is when the motor revs up freely on it's own. Preignition is taking place in which no spark is needed. A red hot spark plug or peice of glowing carbon preignites the fuel mixture and causes engine to continue picking up speed until failure.


To prevent, proper carb adjustment, cylinder and rings decarb, don't rev up on muffs or in neutral at any time.