classic RUNAWAY

[tashasdaddy]

this is a tread i thought should be brought up, the heading not getting much attention. but for educational purposes i did this

http://forums.iboats.com/showthread.php?t=194958

 

[F_R]

Re: classic RUNAWAY

Ah, it's about time somebody asked that question about runaway. Usually they ask what that switch is for on the side of the powerhead--the one they took off and threw away because they didn't need it.

That is a vacuum cut-out switch. The switch senses a runaway condition by monitoring the vacuum inside the intake manifold. When that happens, the switch closes and shorts out one side of the magneto, killing the spark on one plug wire till the motor slows back down.

The switch has to be wired correctly and the starter safety switch has to be there too, or it won't work.

 

[BoatBuoy]

Re: classic RUNAWAY

From the Johnson Service Manual:

"Conditions under which the cut-out functions to limit maximum idling speed are as follows: If when running at fast idle in neutral (2000 RPM or more), the throttle is suddenly closed, a surge or sudden increase in manifold suction is introduced. Under influence of abnormal manifold suction in this instance, the fuel vapor mixture is not consistently ignited but will tend towards firing erratically (as combustible mixtures form*) to result in irregular but excessively ?strong? power impulses to sharply increase motor RPM?s even though the throttle is closed ? Resultant high motor speed (RPM?s) cannot under the circumstances be otherwise reduced or controlled by simply closing the throttle and since no manually operated ground switch is employed, other means are required ? thus, the automatic cut-out..."

 

[kenmyfam]

Re: classic RUNAWAY

Now that is scarey. I do not like running on muffs at the best of times as I always feel that it is not getting enough water supply. Have thought about putting a double hose connection on (one each side) to increase the flow but do not really know how effective that would be. In the meantime I make sure it starts on the muffs, run it for about 30 seconds to 1 minute and then its off to the lake where I know there is without doubt enough cooling water available !!!
Thanks for the post, it certainly gets the point accross.

 

[ezeke]

Re: classic RUNAWAY

Over-reving in neutral can cause a runaway. It does not matter specifically if you are on muffs or at the dock.

 

[rajabatis]

Re: classic RUNAWAY

Ah, it's about time somebody asked that question about runaway. Usually they ask what that switch is for on the side of the powerhead--the one they took off and threw away because they didn't need it.

That is a vacuum cut-out switch. The switch senses a runaway condition by monitoring the vacuum inside the intake manifold. When that happens, the switch closes and shorts out one side of the magneto, killing the spark on one plug wire till the motor slows back down.

The switch has to be wired correctly and the starter safety switch has to be there too, or it won't work.

Hi Thanks for the replies. I'm the guy that posted the original overheating/runaway post on the Evinrude motor.
I got hold of a compression tester and both cylinders test out okay much to my relief. I have ran the motor briefly again o the muffs without the T-Stat and with the stat hole plugged up to check it out and it seems okay.
Ref the switch you talk about my first thought when it went haywire was to pull off the plug leads. I did that and it made no difference. Something was obviuosly creating the combustion process other than a spark.
As I said in the original post I eventually stopped it by choking the motor. I was in such a panic though after switching the ignition off and pulling the plug leads and it kept running, I didn't know what to do next. When the thermostat housing melted and popped out I was in two minds wether to run and hide or try something else! Luckily my brain kicked in and I choked the carb and it stopped. It sat there silent at last, smoking like a dead monster. What a relief!
So how to stop it happening again?
Do I only flush on muffs at tickover for a minumum period?
Or is there other options to prevent a reocurrence?
Thanks again.

 

[ezeke]

Re: classic RUNAWAY

The first thing to do is decarb the engine. Your choice as to method, but I use the one attributed to Capt. Dunkelberger:

" Do-It-Yourself Engine Tip; A Simple and Cost Effective Way to De-Carbon an Outboard By Capt. Bob Dunkelberger dunk75@comcast.net This works for Carbed, EFI, Ficht, HPDI, Opti-max and even 4-strokes... and should be administered after every 50-60 hours of use.

First you need a separate small fuel tank. One of those 3-gallon red Tempos works well or an empty gallon milk jug in a pinch, but it might be a bit messier.

I use Seafoam over the OEM (original equipment manufacturer) stuff like OMC Engine Tuner or Mercury Power Tune. Note: in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that? Seafoam does the job in 15 minutes and can be purchased from NAPA, Car Quest or other auto stores.

You'll need 3/4 gallon of gasoline and one 16oz can of Seafoam for each engine. Don't forget to add 3oz of oil if you are pre-mixing in a carbed engine. Use a 3 ft piece of fuel hose off the small tank. Connect this tank to your engine by pulling off the main tank fuel hose from the intake side of your water separating fuel filter and plug the hose off the small tank onto that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If your engine has a fuel plug then you will also need a fuel plug on the smaller tank's hose.

Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she gets loaded with the Seafoam. Run the engine 15 minutes at the dock or just cruising around under 2500 rpm's. Then shut it down and let it sit for another 15 minutes.

Restart the engine; the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 more minutes. If she smokes after the second time do it again.

I've never seen one still smoke after three doses. (I bought a Bronco two years ago that had 95,000 miles on it. When I used Seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke)

The gallon mix should be just enough to do this 3 times. You don't need a wide-open throttle and you don't need to change the plugs. The plugs are cleaned at the same time as the combustion chambers. My suggestion is that every 50-60hrs is the optimal time to change plugs in most engines.
I cleaned an antique Evinrude once that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the aforementioned mix through it.

Seafoam, a great product, has been around since the 1930's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards.

For you guys with the 4 stroke outboards? Those engines work 10 times as hard as any auto engine ever will and they too will carbon up. Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2-stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne.

For those guys that like to work the carbon treatment by spraying it down the carbs, Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure and notes on the can, "Oxygen Sensor Safe". After that, if your engine manufacturer recommends a daily additive treatment then do so. The tank and hose are a one-time purchase and the Seafoam is only costs $5-6.00 per can."

Note: Capt Bob Dunkelberger is a Marine Surveyor in New Jersey. dunk75@comcast.net
​

 

[F_R]

Re: classic RUNAWAY

If it continued to run with the plug leads pulled off it must have been dieseling. Probably from being too hot or hot carbon in cylinders. Whatever, it should never have gotten that hot. Especially since it melted the thermostat housing. That is way, way, too hot. Lucky you didn't burn up the motor...or maybe you did? What, exactly, are you using for "muffs" ? The regular earmuff style things won't work on a big twin series 35-40 hp. The correct "Flushette" is getting pretty hard to find.

 

[rajabatis]

Re: classic RUNAWAY

If it continued to run with the plug leads pulled off it must have been dieseling. Probably from being too hot or hot carbon in cylinders. Whatever, it should never have gotten that hot. Especially since it melted the thermostat housing. That is way, way, too hot. Lucky you didn't burn up the motor...or maybe you did? What, exactly, are you using for "muffs" ? The regular earmuff style things won't work on a big twin series 35-40 hp. The correct "Flushette" is getting pretty hard to find.

Agreed it should never got that hot but not a lot of use shutting the stable door after the horse has bolted eh? It had been flushed regularly over the last year with no problems. So I was not aware or expecting there would be a problem this time!

The original question was why did it happen? And this one how to prevent it?
If you re-read my post I did say I had checked the compression since the event" and ran the motor again. It was okay. Tough motor that old Evinrude.

Cooling was a set of double inlet muffs connected to a high pressure hose. I couldn't get a much better flow through that engine on muffs!

 

[rajabatis]

Re: classic RUNAWAY

Thanks eseke for that advice. I'll do something along those lines asap.

 

[F_R]

Re: classic RUNAWAY

OK, sorry, Somehow I had the impression we were talking about an older 40hp here. I suppose because of the runaway thing, a 35-40hp trait. You can disregard my comment about the vacuum switch too.

Muffs it is for your 50hp.

 

[tashasdaddy]

Re: classic RUNAWAY

thought this could use a bump. been a while since it's been up.

 

[adrock430]

Re: classic RUNAWAY

I had a similar issue this weekend, and I'd like to try and avoid this happening again, but I don't have a vacuum cut-out switch (so it seems)...how would I go about installing? I have an 88 force 50 hp.
Thanks! Adam

 

[bob1340]

Re: classic RUNAWAY

When I was a kid many years ago I saw a newly rebuilt GMC 4/71 diesel runaway. It was an amazing site. This was the first fire uhearted the rebuild and the guy had something screwed up with the rack linkage that controled the injectors. These are 2 stroke diesels and once that sucker got up to 4,000 rpm or so all hell broke loose. The blower was putting out so much pressure it was blowing gaskets left and right as the poor guy was trying to get it shut down. It threw a rod after about 20-30 seconds of running at high rpms. We had the crank shaft throw welded and reground, bolted a 6" square plate of 3/8 steel with a gasket to the hole in the block, put a new rod in and used the tractor another 25 years!!!