Motor Runs Away!!! Unusual Situation!

[chodie]

1992, 40 HP Johnson. Cranks excellent. Idles OK; Give it the throttle it goes in gear , then motor Reves up to a very high speed. Pull throttle back and it still stays reved up. The butter fly valves are closed while this is going on. The ignition switch will not shut the engine down, the emergency switch will not shut the engine down. The only way to kill the engine is to disconnect the gas line and let all the fuel be consumed. Thank goodness this happened while I was getting the motor ready for fishing and I was using a Muff for water. I repeated this several times and the same thing happened. If I had been on the lake I might not be writing this. Please help if you can. I am now afraid to put the boat in the water.

 

[iwombat]

Re: Motor Runs Away!!! Unusual Situation!

Check the linkage to your timer base. Sounds like it's no longer connected.

 

[F_R]

Re: Motor Runs Away!!! Unusual Situation!

Put it in gear and it runs wild? Sounds to me like your propeller hub is shot. As such, you are able to rev it up with no load on it.

 

[tashasdaddy]

Re: Motor Runs Away!!! Unusual Situation!

either is possible. make sure you timing plate is not sticking, sounds like it is out of sinc.

 

[JB]

Re: Motor Runs Away!!! Unusual Situation!

Turn off ignition and it won't stop? On muffs (no load on the prop).

Thermal runaway. Not at all uncommon when an engine is revved without a load. You are very fortunate the engine did not grenade on you.

That would not have happened in the water because you would have had a load on the prop.

Check your timer stator, as iwombat suggests. It may have stuck in an advance position or it may be loose.

NEVER rev a 2 stroke without a load on it. Explosions are not unheard of.

 

[Rick.]

Re: Motor Runs Away!!! Unusual Situation!

You might be able to shut it down by applying full choke. Rick.

 

[mrimike]

Re: Motor Runs Away!!! Unusual Situation!

sounds like an air leak.
its glow plugging.. pretty much running on heat.. believe it or not best way to get it to quit is to pull choke and suufocate it
had this happen on seadoos.. even pulling the plug caps off it will still run

 

[F_R]

Re: Motor Runs Away!!! Unusual Situation!

1992, 40 HP Johnson. Cranks excellent. Idles OK; Give it the throttle it goes in gear , then motor Reves up to a very high speed. Pull throttle back and it still stays reved up. The butter fly valves are closed while this is going on. The ignition switch will not shut the engine down, the emergency switch will not shut the engine down. The only way to kill the engine is to disconnect the gas line and let all the fuel be consumed. Thank goodness this happened while I was getting the motor ready for fishing and I was using a Muff for water. I repeated this several times and the same thing happened. If I had been on the lake I might not be writing this. Please help if you can. I am now afraid to put the boat in the water.

QUOTE: Thank goodness this happened while I was getting the motor ready for fishing and I was using a Muff for water. QUOTE

----OK, after re-reading this tale, I take back my prop hub comment. I thought you had it in the water. The water would have put a load on the prop.

QUOTE: Give it the throttle it goes in gear , then motor Reves up to a very high speed. Pull throttle back and it still stays reved up. QUOTE

----OK so you put it in gear and the motor revs up to a high speed, then PULL THE THROTTLE BACK and it stays reved up. It didn't rev till you put it in gear. If you pulled the throttle back to try to slow it down, how did the throttle get pushed forward to rev it up in the first place??

QUOTE: I repeated this several times and the same thing happened. QUOTE

----OK, that clinches it, you tried it several times. Tried what several times? Pushing the throttle forward to rev it up?

By now it is obvious that you are deliberately doing this yourself. Unknowingly, but deliberately. Stop revving it up without a load on the prop!!!!! You are causing your own situation, thermal runaway.

It was designed to run on a boat in the water, not on a trailer with muffs and revving the daylights out of it. And unless it is a chainsaw, never rev any engine to high RPM without a load on it.

It ain't broke, so don't fix it.

 

[tashasdaddy]

Re: Motor Runs Away!!! Unusual Situation!

never rev above 1500 rpms on muffs, or you can get a runaway. i have had the runaway in the water, in neutral, the throttle linkage and remote cable were way out of adjustment.

 

[CharlieB]

Re: Motor Runs Away!!! Unusual Situation!

Pull throttle back and it still stays reved up. The butter fly valves are closed while this is going on.

??????????????

Pull the plugs, this way I KNOW you wont be starting it.

Now, put it in gear and open the throttle all the way. Look at the butterflys to be sure that they are flat, perfectly wide open.

Now, pull the throttle back to neutral, idle. Check the throttle linkage/lever at the carbs. Is the timer idle set screw against the stop? Can you pull the linkage back ANY AT ALL? Is the carb llinkage/roller actually in contact with the throttle cam?

It should NOT