450 gas

metalmender · May 21, 2012

can anyone tell me what makes a motor want to sit and continue running after the key is turned off, I guess they call it "dieseling" I know the ignition is dead after turning the key off but it wants to continue running after I shut it off after a good workout when the weather is warm,After plowing 17 acres 2 weeks ago, I turned it off and it did just that until the crankshaft broke, I got the new crank and am planning on installing this week but dont want it to happen again, any suggestions

rufus80 · May 21, 2012

Timing issue

Heat Houser · May 21, 2012

Your spark plug electrodes are likely glowing red hot and are igniting the fuel causing run-on. Change to cooler heat range plugs if you are going to work it hard in warm weather. The electrodes of a "hot" plug protrude futher out of the bottom of the plug to move it away from the threads in the head. The head threads act as a heat sink so sticking further out from the heat sink, hotter plug. They also play games with electrode size as well....

mike1972chev · May 21, 2012

You broke a crankshaft???? WOW! IDK if I would blame all of the "dieseling" for the broken crank???

I TOTALLY agree with checking the timing. I wouls also look at all of the mechanical advance parts inside the distributor for wear,breakage.

Things to look for in your "teardown".Excessive carbon build up on piston tops and combustion chambers/valve faces.

ALSO,what was LOW idle set at on this engine?????? If it is set TOO high,THAT will cause "run on"".

If you had a REALLY high compression motor on "cheap" fuel,it will "run on" sometimes.

I am betting that Crankshaft was "stress fractured" for a way long ,long time before it broke???

CNKS · May 21, 2012

Could be timing, could be a hot piece of carbon in one or more of the cylinders. Whatever you do, kill the engine either by letting out the clutch while in gear, or pull the choke out. Some say I am washing the oil off the cylinder walls with the choke out, but it's better than breaking the crankshaft. You might pull the head and clean the top of the pistons off. Keep it simple to begin with by timing it correctly, although I doubt if that is the problem.

robgIN · May 21, 2012

I would be more inclined to go with the the glowing carbon or spark plug theories. Shouldn't matter what the timing is when the spark is shut off, however poor timing can contribute to the excessive combustion chamber temp. Try letting it idle for a few minutes to cool down before shutting it off, and if needed put it in hi gear and hold brakes and let out on clutch when you shut it off.

the tractor vet · May 21, 2012

Ya got the wrong plugs in it , the timing is off and you are running cheap fuel. And she is running to hot.

Bob M · May 21, 2012

Definitely is NOT ignition timing. (Once you turn off the switch there is no ignition, hence there can be no "timing")

Most likely a combination of things others have pointed out: Hot plugs, glowing carbon deposits, hot engine, low octane gas, etc. Excessive compression (LPG head) can contribute too.

Stuff you can do to minimize dieseling the future:

- Set the slow idle RPM as slow as possible (400 RPM or less for a 450)

- Adjust the carb idle mixture for smooth idle then reset it a quarter turn or so rich.

- Use cooler plugs (Champion D-17 or other mfr's heat range equivalent).

- After working the engine hard, let it run at slow idle 5 minutes or so to cool before hitting the switch. Or simply close the fuel shutoff at the sediment bulb and let carburetor run out of gas (don't forget to turn off the ignition afterward however!)

- When shutting down, put the transmission in road gear and hold the brake. With the engine at slow idle gradually let the clutch out until the engine just starts to pick up the load then shut off the ignition. The engine WILL stop immediately!

the tractor vet · May 21, 2012

AH if the timing is off this will cause combustion temps to rise and this will contribute to engine run on , also a to lean mixture will cause this . And also to fast idle . Now not knowing what has been done to this engine in the past or what oil is used or amount of oil burnt will also cause carbon deposits to glow . engine temp as if running to hot. since neither of us can see , hear or run this tractor all any of us can do is GUESSTAMATE . WE do not know if this tractor has the LP head or the high alt. pistons . Heck who knows it may have been one of the many that i put them pistons in years back .

the tractor vet · May 21, 2012

IT DOES when the spark plug is glowing like a glow plug due to the timing being off. and you do not know how many times that i have seen the timing off from some wizz kid setting it by EAR.

Andrew Z · May 22, 2012

Run mid grade fuel, my 450 will do the same; for me i need 93 but have some engine work as well.

Andrew

Ellis Kinney · May 22, 2012

I always put the transmission in 5th gear before I push the kill switch. If it starts to diesel let the clutch out with the other foot on the brake. It won't buck or jump. Ellis

rtb321 · May 22, 2012

sounds like you have a super m. mine will do that after working it hard if i use cheap gas. put premium in it and it will stop. colder plugs won't help. just make sure you pull a plug out and make sure it's not burning too lean. that can cause it to run on too.

450 gas

metalmender

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rufus80

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Heat Houser

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mike1972chev

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CNKS

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robgIN

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the tractor vet

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Bob M

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the tractor vet

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the tractor vet

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Andrew Z

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Ellis Kinney

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rtb321

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