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Discussion Starter #1
Hello,

While searching for a forum I came across several post in which people were seeking advice for how to stop there mower engine from running on after the iginition has been turned off. The cure is simple and requires no skill. Just leave the throttle wide open when you turn the ignition off. By doing that the fuel to air ratio is to rich to ignite.

LawnRon
 

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I understand what your saying,but some run on because the ignition is not being interrupted completely!what your describing works for detonation where a burning valve,too hot plug range or carbon deposit is igniting the mixture and the extra fresh fuel/air cools it below ignition temp.!a manual choke applied works too but will cause cylinder washdown and eventually oil contamination!but your really just prolonging an underlying problem,that is going to cause more serious issues if it's not resolved!my.02
 

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Discussion Starter #3
donmac,

but your really just prolonging an underlying problem
Both of my Kohler Command powered Grasshopper mowers had the 'run on' problem from day one. It is the nature of a 4 cycle engine to 'run on' due to detonation when the combustion chamber temperature is high and the air to fuel ratio is lean.

Chances are that you're to young to know that GM engines use to have a solenoid that would retract when the ignition was on and would extend when the power was turned off. When extended it held the throttle above an idle which accomplished the same thing that I'm suggesting.

GM was not prolonging an underlying problem nor am I.

LawnRon
 

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seems to me this was about the time Gm was coming to grips with emissions and unleaded fuel! combustion chamber temps should never be so high to promote preigntion! now that I think about it probably the reason my 78 olds rattled so bad!
 

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Discussion Starter #5
donmac,

combustion chamber temps should never be so high to promote preigntion!
What do you suggest? Perhaps running water on the cylinder heads prior to shuting the engine off?

You can defend your position on this subject but, the facts are that it occurs with new engines that are operated within the manufacturer's specifications and have not ran long enough to have a carbon build up.

General Motors started using the throttle solenoids in 1967. The idea came from Zora-Arkus Duntov and it was based on his personal experience with racing engines.

LawnRon
 

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I would suggest running a fuel mixture that keeps combustion temps a little cooler!stoichiometric air/fuel is great for power/ emissions,but sometimes drivability and longevity suffer!
If I owned an engine that wouldn't shut off with the Key- I'd wonder why it had a key!:ROF! I'd fix it!
 

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Discussion Starter #7
I would suggest running a fuel mixture that keeps combustion temps a little cooler!stoichiometric air/fuel is great for power/ emissions,but sometimes drivability and longevity suffer!
If I owned an engine that wouldn't shut off with the Key- I'd wonder why it had a key!:ROF! I'd fix it!
I offered a reasonable solution for a common problem and it in no way harms the engine. If you disagree with my suggestion then feel free to go ahead and outline the procedure for altering the fixed jet in the carburetor to enrich the air fuel ratio at and idle. Pictures would be nice.

I have built blown alcohol 364ci small block Chevrolet engines that propelled my dragster to 240 MPH in 6.02 seconds back in 1977 and 1978 and from 1979 to 1984 raced Go Karts that hit speeds as high as 160 MPH with engines that I prepared. Believe me I could and would alter the carburetor if it was required but, it is absolutely not required.

LawnRon
 

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I recall a gm solenoid that worked the reverse of that described .when running it was extended to point of normal idle holding throttle plate slightly open . when key went off it retracted and aspring pulled throttle plate completely shut to prevent run on
 

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Discussion Starter #9
38racing,

You are correct. I had it backwards. I guess that principal could also be used on small engines by setting the idle down to a point where the engine would not idle. However my suggested technique requires no tinkering with the engine settings.

LawnRon
 

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I recall a gm solenoid that worked the reverse of that described .when running it was extended to point of normal idle holding throttle plate slightly open . when key went off it retracted and aspring pulled throttle plate completely shut to prevent run on
38, you're right. All the GM idle solenoids I ever saw worked exactly as you describe. WOT won't help as venturi vacuum and venturi air velocity determines air/fuel mixture so even if the spark plug isn't firing the air fuel mix is still optimum whatever the RPM is.
Mike
 

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this is all a moot point, governed engines, like ALL mower engines, automatically flip the throttle blade wide open as soon as spark is killed and the engine begins to slow, so it doesnt matter is your dash throttle control is at low idle, or wide open...the throttle blade will be wide open regardless.

After-run solenoids have been standard issue on riding mowers for over 15 years now, and "after-run" has become a less common issue, however backfires have increased on some models due to thin mufflers, and lean conditions.

Most manufacturers will suggest to idle the engine for 30 seconds prior to shut-off, in an attempt to lower Exhaust temps, and allow for less intake/exhaust strokes to push fuel onto the hot muffler, to prevent backfires.

After-run is a condition caused when carbon on the valves, piston, head, plug..is hot enough to ignite fuel, after the engine has been turned off...its common on engines that are shut down immediately after a hard run...with no anti-diesel solenoid in operation...
 

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I too remember the GM throttle position solenoids. If they died, the engine would not idle. Throttle plates completely closed choked it pretty quick. Otherwise it would cough and stumble and generally make a lot of noise until it stopped. Noxious fumes produced also, which defeated the purpose of all the merde that was being attached to reduce emissions.
I thought the idle-down procedure was to lower rpms such that the engine would not have enough inertia to spin over so many times after the ignition was killed.
I have left the blades engaged, and the throttle moved towards idle in an attempt to add some load and prevent excess revolutions feeding un-burned fuel mix into the engine & muffler. It rattles a bit as it slows, but doesn't run-on.
tom
 

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Discussion Starter #14
this is all a moot point, governed engines, like ALL mower engines, automatically flip the throttle blade wide open as soon as spark is killed and the engine begins to slow, so it doesnt matter is your dash throttle control is at low idle, or wide open...the throttle blade will be wide open regardless.
Your statement is contrary to reality.

From day one both of my Grasshopper 725 mowers would run on detonation after the ignition had been turned off but, only if the throttle was set to the idle position. They would ignite at least 6 times before coming to a stop. With the throttle left wide open they do not back fire or run on detonation. Both of my mowers have over 1000 hours of use and they require no additional oil between oil changes. I consider that to be proof that my shut down procedure does not harm the engine.

Your statement regarding a cool down period is correct. However most people, myself included are more concerned with their own cool down period.

I offered a reasonable solution for a common problem. The solution requires no tools, technical knowledge or mechanical experience and it is time tested.

LawnRon
 

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Your statement is contrary to reality.

From day one both of my Grasshopper 725 mowers would run on detonation after the ignition had been turned off but, only if the throttle was set to the idle position. They would ignite at least 6 times before coming to a stop. With the throttle left wide open they do not back fire or run on detonation. Both of my mowers have over 1000 hours of use and they require no additional oil between oil changes. I consider that to be proof that my shut down procedure does not harm the engine.

Your statement regarding a cool down period is correct. However most people, myself included are more concerned with their own cool down period.

I offered a reasonable solution for a common problem. The solution requires no tools, technical knowledge or mechanical experience and it is time tested.

LawnRon
I cant explain your situation, but I can say with absolute certainty, the throttle blades wil lbe wide open, rather it is shut off at idle, or full throttle, as these engines have a governed idle. The theory that there is a rich fuel mixture if turned off at full throttle is false, as a rich fuel mixture would make it more likely to after-fire and run on.

Oddly enough, when i was running race karts, we were running taped up cooling shrouds, HOT plugs, missing flywheel fins, etc...to get our temps up to a maximum safe range, and when the karts came off the track, they were generally running temps about 100* higher than any mower engine...glowing exhaust pipes, shut em off, and I newer recalled hearing a single one run on or backfire.

It is possible that when shut off at full throttle, the air being forced through the engine as it winds down, cools parts enough to prevent run on...however as said, a short 30second idle should give time for hot embers and parts to cool adequately....
 

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Discussion Starter #17
To all who chose to argue with me about my suggested method for avoiding ron on due to detonation after switching the ignition off.

1) Open this link: http://kohlerengines.com/maintenance/faqs.htm

2) Go down to this FAQ: Why does my engine backfire when I shut it off?

3) Read the answer in the drop down caption.

4) Contact Kohler and argue with their technical support department.

It's been fun,
LawnRon
 

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Backfire is not after-run.

Backfire is an explosion in the exhaust when the engine stops, afterun is when the hot combustion chamber continues to ignite fuel after the ignition has been turned off. Two TOTALLY different symptoms...
 

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Backfire is not after-run.

Backfire is an explosion in the exhaust when the engine stops, afterun is when the hot combustion chamber continues to ignite fuel after the ignition has been turned off. Two TOTALLY different symptoms...
Right on .after running we called 'diesling' because engine was running without a spark. i have had a bunch of mowers (much to the wife s displeasure) and never had one diesel
 

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Ive had a couple diesel...one was a Kohler K181S, after a hard pull when i used my little WH 702 to pull a disabled 3000lb Farmall C with flat tires, down the road in 2nd and 3rd gear. It operated at 100% duty cycle (governor wide open) for 5-6 minutes straight, the paint on the block was smoking, the 1" stack was popping off rust and paint onto my leg...

When i shut it down to unhitch the tractor at its new location...the engine continued to run for about a minute. No damage...I pulled the engine down to inspect it and there was no wear or damage, and virtually no carbon left at all...

Then I had a 13.5 Briggs OHV...after 4-5 minutes of running, when shut down, it would stop and proceed to run backwards for a few seconds...rather it was shut down at full throttle, idle, half throttle...or partial choke...didnt matter.

I found that it had a bad switch, i put in a new one and it suddenly stopped...strangest thing ever.
 
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