Garden Tractor Engine Problem

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I have a 15 Hp Simplicity garden tractor with a Kohler engine. This machine is about 13 years old and I have had it since it was new.
I went out to mow the grass this weekend and the engine died on me after about a half an hour. It just suddenly stopped and made a couple of small back-firing noises.
I noticed it did still have a few inches of gas in the tank but I topped off the tank with fresh gas anyway. But before I put more gas in it I took off the fuel filter and noticed there wasn't much gas flow from the tank. I blew out the filter with air pressure and re- installed the fuel filter. It still wouldn't start even after adding more gas to the tank.
I poured a little bit of gas in the carburetor and it still wouldn't fire. I spent some time trying to get the hydrostatic transmission release lever to disengage so I could push it back into the garage but never got that to work so I left it alone for a while.
After a few hours, I went out and it started right up. It ran good for 15 minutes and then quit again. I left it in the yard until yesterday morning. It started right away and I pulled it into the garage. While I was out and about yesterday, I picked up a new fuel filter and installed it just in case that would help.
I started mowing the yard with it again today and had the same problems. It ran good for about a half hour and quit. I waited a few hours and it started and quit again after about 15 minutes.
I was very hot Sunday when this started but not as hot today and even cooler this afternoon. But I'm still wondering if it has a vapor lock problem.
Anybody got any more ideas I can try?
Thanks, David
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Check if it gets spark just after it dies, you know how, pull plug wire and get it close while someone tries to start it, ive had coils and ignition modules fail only when hot, then completely fail later. Look at it run in dark with the coil exposed if possible , mine had a crack and I could see it arching to ground, a new coil also gave it more power.
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That sounds like a problem I had with a John Deere. It turned out to be the fuel tank was full of crap in the sump where the pickup tube operates. I had to pull the tank and flush it several times to fix it, but now it runs like a deer.
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wrote:

#That sounds like a problem I had with a John Deere. It #turned out to #be the fuel tank was full of crap in the sump where the #pickup tube #operates. I had to pull the tank and flush it several times #to fix it, #but now it runs like a deer.
I bought a new Deere and it did the same thing. They took it back and changed the seat. Told me the seat switch was bad.
They first told me it could be trash in the gas. I doubted that as I bought a new 5 gallon gas can and filled it up on the way home. The gas was less than an hour out of the pump. If it was any bad stuff in the gas it had to come from the Deere place and be the small ammount they used to deliver it with.
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Gas in the carb rules out the cruddy tank option. I'd suspect heat related problem. Bad ignition coil insulation comes to mind. Also option of valve seats may be burned, and the valves aren't completely closing with a hot engine. Much less likely is burnt to death motor oil.
The diagnosis needed, is to get the engine hot enough to fail. Pop the spark wire, and check for spark (ask, if you don't know the procedure). Also check for compression while the engine is in failure. That will help determine if it's spark or valve problem.
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hibb wrote:

You fuel line is clogged and the tank is probably full of crap. Are you careful not to let the dirt and grass from the top of the can fall into the tank when you fuel up? That's what people do. Fill the tank full of crap and wonder why it stops running.
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If that's the case, why does it run fine after it cools off, until it gets hot again?
That points to an electrical problem, not a fuel problem. To the OP: the problem is almost certainly in the electronic ignition module. Replace that, and the problem will go away.
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Doug Miller wrote:

If the tank was run near empty, drain the carb bowl and the fuel pump as they probably have water in them now. It may not be the whole problem, but it's one I've seen before and a good starting point.
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On Aug 19, 8:03am, snipped-for-privacy@milmac.com (Doug Miller) wrote:

I can only offer that the crap moves around, & will settle once the 15 minutes has passed. Mine did exactly what the OP describes, sometimes it would run and mow 15 - 30 minutes, sometimes it wouldn't make it out of the garage. My final diagnostic tool was a spare tank salvaged from a long dead mower. I hooked it up in the console area and filled it with gas. The mower came to life instantly & mowed for a solid hour, at which point I took it to the shop and pulled the fender assembly and removed the tank. An amazing amount of crap came out. I used diesel as a solvent, & followed up with compressed air, other methods would likely work as well
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On my vehicle, the tank fill cap is under the seat and stays pretty clean. I am going to check the plug for spark first but I will keep what you said in mind too if I don't see a problem with the electrical.
Thanks, David
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Lets hope the OP tells us what he found. Either could be a cause of this problem. Since he tried a splash of gas, I'm doubting fuel problems.
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On Wed, 19 Aug 2009 13:03:17 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

I have a John Deere tractor with a Kohler engine. It did almost the exact same thing as yours. Its start up , run for a few minutes and then lose power and run rough. Let it sit for a while and it'd do the same thing.
It cost $250 to replace one of the coils. I guess there are 2 coils with associated electronics. One of them died under high temps.
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dicko wrote:

Y'know, I just don't think they are making ignition coils that are as good as the ones from way back when.
I drive a 2004 6 cylinder engine Lincoln LS with less than 45K miles on it and during the last year I've had to replace all 6 of the coils under the hood
Well, maybe my trusted auto mechanic might have replaced a couple of "still OK" coils in the process, but I had to bring the car into his shop three times during the year, when the engine began stumbling under load again, to get yet another coil replaced.
Jeff
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I hope that new coil had gold plated contacts, and that you got kissed after you paid the bill.
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On Aug 19, 9:03am, snipped-for-privacy@milmac.com (Doug Miller) wrote:

I appreciate the other suggestions and will take them seriously but I think I will start with what Ransley suggested and check run it until it stops again and check if it is getting a spark.
The reason I want to do that first is because it would not fire up at all when I poured a bit of fuel right into the carburetor. If it is getting a spark, then I will go back to the possibility of a fuel supply problem.
Thanks, David
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Doug Miller wrote:

That's because the fuel is running slowly and slowly fills the carb and lines. You suck it up faster than it flows so you only get 15 minutes.
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[...]
Absolute nonsense. There's only enough fuel in the carb and lines to keep the engine running for 30 seconds, tops. If the fuel flow were restricted enough to cause the problem, there's no way the engine would run half an hour (as the OP described) -- more like half a minute.
The problem is his electronic ignition module.
To the OP: to diagnose this, when it won't start, check to see if the engine has spark. I'm betting it won't. Locate the electronic ignition module, then spray some starting fluid (ether) on it -- that'll cool it offf in a hurry. Might need to hit it two or three times. Check for spark again -- if you see a spark, you just confirmed my diagnosis. If you don't see a spark, that doesn't mean the problem *isn't* with the module -- could be you just didn't get it cool enough.
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Doug Miller wrote:

Not likely, they either work or they don't at all.

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So, why didn't it run with a splash of gas into the carb?
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Even if you see a spark it could be to weak to fire under load, ive have motors that idle but missfire when given gas, so a weak spark is still bad.
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