RPM's went crazy -1994 40 horse Johnson

[purplesage]

I have a new to me motor that has been sitting without running since 2002 and only had 50 hours or so on it before that. It has/had VRO and is electric start. Not sure what the previous owner had done but the VRO had been leaking for a long time so the bottom of the motor had a plastic bag around it to catch the slow leak.

Following everyones instruction I decided to rebuild the carbs even before attempting to start. It turned out the bowls on both carbs as well as the fuel filter and fuel lines were full of oil. After cleaning all that out - rebuilding the carbs and removing the VRO it was time to turn it over.

The motor started after turning over a few times but then died. I primed by pumping the bulb and started it again. It would run for a bit but then die. I then ran it for a bit by choking as soon as the RPM's would begin to slow. The motor then began to run so I thought I was doing OK but then the RPM's started climbing. I turned the key off and the motor continued to run with the RPM's increasing at an alarming rate. I then pulled the kill switch. No help. I then removed the fuel line - it took a bit but the motor did eventually die.

I started it a couple times for short periods of time - it runs but is back firing.

I obviously has cable issues but am confused by the fact the motor wouldn't quit. Do I also have electrical issues.

All advice appreciated - Jon

 

[HighTrim]

Re: RPM's went crazy -1994 40 horse Johnson

Was this on the muffs in the driveway?

 

[purplesage]

Re: RPM's went crazy -1994 40 horse Johnson

Yes it was - I did have water coming through the telltale during the episode but I am going to redo the water pump because I am worried.

 

[SeaKaye12]

Re: RPM's went crazy -1994 40 horse Johnson

Do a search here on "runaway engine"

Can be very scary.

Chuck

 

[tx1961whaler]

Re: RPM's went crazy -1994 40 horse Johnson

The motor went into thermal runaway, which is usually caused by over-revving it while not under load. The neat part is that you could have pulled the plug wires and it would have still kept running...... with the older 40's you can just flip on the butterfly choke and it will die out. Or stuff a towel in the carb throat.

 

[HighTrim]

Re: RPM's went crazy -1994 40 horse Johnson

What likely happened is at stated, your motor went into thermal runaway. That is the reason that you can only run your motor at idle while on the muffs, without a load. It can be very dangerous. As you found, turning off the key or pulling the lanyard has no effect, you need to starve it of fuel, which sometimes can take too long. You were lucky actually. What happens is that bits of carbon in the cylinder ignite the incoming fuel/air charge. For future reference, the quickest way to kill it is to hold you hand or a rag over the carbs air intake, no oxygen/no fire.

I would check compression, and possibly pull the head to visually inspect cylinder walls.

 

[boobie]

Re: RPM's went crazy -1994 40 horse Johnson

Agree with all above. Had it happen to me and the best way to stop it is the rag in the carb air intake trick.

 

[purplesage]

Re: RPM's went crazy -1994 40 horse Johnson

Live and learn - now I Have to hope I didn't fry the power head. One more question though - can you test run the motor in a tank of water or must it be in a larger volume of water to have sufficient back pressure. Also, assuming I fried the water pump is it likely that parts of the impeller went all through the motor? Just trying to figure out my next steps. I have read several write ups about thermal runaway which helped me understand what happened but none of them talked about the next steps. Again - thanks for the heads up. Jon

 

[jonesg]

Re: RPM's went crazy -1994 40 horse Johnson

It hasn't been run since 2002, don't be in a big rush to run until you go through the steps to awaken it.
Decarb it, do a compression test.
Change gear oil etc etc.

See the sticky file "top secret" awakening a sleeping outboard.
Heres the link, no-one ever reads it until too late.
http://forums.iboats.com/showthread.php?t=299680

 

[purplesage]

Re: RPM's went crazy -1994 40 horse Johnson

I appreciate the info and jonesg I actually thought I was doing the steps (as described in the awakening) just thought I could test it with the muffs. My problem was I had always done that with IO's and didn't realize I could end up with the problem I did. A hard lesson but not a mistake I will repeat.

I am still wondering about the tank question. Once I rebuild the water pump to undo any damage I did yesterday is it OK to test run the motor in a tank as opposed to doing the work at the lake? My thought was to use the big garbage can on wheels used for the weekly pick up. It is certainly over 100 gallons and plenty deep. Filling it will be slow and I will have to empty it with a siphon but I thought it might work - just don't want to make another mistake. If I get second chance here (meaning I didn't fry the motor on with the first mistake) I don't want to blow it but I would like to keep making progress on the boat. It is still winter here so it is too soon to take it to the lake.

 

[jonesg]

Re: RPM's went crazy -1994 40 horse Johnson

Yeh the pump just has to be submerged, i went through that with my 10 hp.
These pumps only push water, they have little draw.
THeres nothing wrong with drilling a drain hole in the trash container when you're done, better to let rain water run out.
You can always plug it to use again.

Watch all the videos on youtube with guys revvin the snot out of the engines on a hose, most people think its the same as a dirt bike.!