Kohler 12.5S stalling

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  #1  
Old 07-27-07, 03:03 PM
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Kohler 12.5S stalling

I am a newbie to this board, and have performed a search on this issue, which in other cases was traced to an incorrect fuel filter. Here is my problem. I have an STX38 John Deere with a Kohler Command 12.5S or 1215. It starts and idles fine, but when hot, and under load, will sputter, spit, backfire and then stall. The fuel filter (which I have since completely done away with) will at that time be empty. I can sort of baby it with the throttle and run it on full choke - for about 3-5 minutes, until it recovers. Shutting off the deck will help, but it still needs time to recover. When it does, it will last 5-10 minutes and begin the process all over. So far, I have replaced all fuel lines, taken apart and cleaned the carb and choke, changed oil, changed plug and air filter, danced around it, and treated it nice. Nothing helped. If it were a car, I'd say fuel pump, but I can't find one. Any help from those more wise than I is appreciated.

Stefan
 
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  #2  
Old 07-27-07, 11:18 PM
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Loosen the gas cap. If the vent in it is plugged, it will vaporlock the fuel system and starve the engine for gas.
 
  #3  
Old 07-28-07, 05:00 AM
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Have tried even running it without the gas cap. Somehow, I think I am getting a type of vpor lock.

Stefan
 
  #4  
Old 07-28-07, 06:10 PM
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Perhaps you are vapor locking and it's as a result of an engine that is overheating due to plugged cooling fins. Have you pulled off the blower (flywheel) shroud to have a look at the cooling fins?
 
  #5  
Old 07-29-07, 05:11 PM
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I took off the shroud and everything looked clean. Nonetheless, I doused the motor in simple green, hosed everything off and then dried with a leaf blower. In the process, I found that one stud on the muffler flange did not have a nut on it. Then I took off the muffler, checked the gasket, and re-asembled with both nuts. Still, after 20 minutes of mowing, same symptoms. Even adjusting the carburator as stated in the manual did not help. AAAAAHHHHHHHHHGHHHH. I think last time I got gas I used 93 Octane. Could this be one of the problems? Thanks.

Stefan
 
  #6  
Old 07-29-07, 09:05 PM
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Remove the carb bowl and let the fuel flow from the carb into a cup. Observe the rate of flow. If it's not a solid steady flow, there is an obstruction. Take the inlet needle out of the carb, and the fuel line off, and spray compressed air through the inlet in reverse (from the inside of the carb out through the fuel line connection). If nothing is revealed there, do the same with the fuel tank connection. I've seen wierd things pluggeing both areas on different mowers. Even on mowers with good fuel filters.
 
  #7  
Old 07-31-07, 02:01 PM
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Do you mean that the tank should simply start to empty through the carb bowl at some fairly steady rate? Surely worth a try. Thanks

Stefan
 
  #8  
Old 07-31-07, 07:02 PM
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Yes, unless this engine has a fuel pump, fuel should flow via gravity all the way to the float bowl. It should be more than a dribble.
 
  #9  
Old 08-02-07, 07:42 AM
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Sounds like you have a plug of fine grass clippings at the fuel pickup in the fuel tank. When you removed the fuel filter because it was always empty, leads me to believe that fuel is not getting that far from the tank. You can remove the fuel cap and blow back towards the fuel tank through the fuel hose. You can remove the tank and lines blowing each out. The Parts Breakdown shows a shut off valve in the fuel line also. Any of these areas fine, string type foreign materials will accumalate and restrict the flow of fuel.
 
  #10  
Old 08-03-07, 06:38 AM
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Although I have not had the chance to try Cheese's removal of the carb bowl, the fuel filter was not empty with the engine cold. I have replaced all fuel lines, and even drained the tank in the process. If there is an obstruction, I suspect it is somewhere in the carb. I'll report back after this weekend. It should be hot enough here in PA (upper 90s with stifling humidity).

Thanks

Stefan
 
  #11  
Old 08-03-07, 10:02 AM
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I had a Cub with a CH12.5S Kohler, that had similar symptoms. It would eventually die however it would start right back up then repeat. This one did have a mechanical fuel pump. It would take between 45 to 60 mins for the symptoms to appear but then would miss and die until it completely cooled.
I replaced the fuel pump and ran it a solid hour with no hassle. Shut it down to chase the dog out of somewhere, came back finished another 5 mins and was putting it up,case closed, when the symptoms returned. I tested for spark each time the engine would not start, but I always had spark. Hook the plug back up and it would start. I finnally just kept the process up until I was able to test for spark and briefly have none, then have it show all of a sudden. This was enough for me to convince the owner to try replacing the coil. I replaced the coil and have not seen it back since. I have serviced other equipment from the same owner since.
Using Internet Explorer, if you go to the kohler site, http://www.kohlerplus.com/login.asp enter as a guest and identify your engine, find the service manual for it and there are steps to test the coil. These tests if failed can and should indicate a bad unit. If it passes all tests, it can still be bad, and should not be eliminated as the problem.
 
  #12  
Old 08-08-07, 07:10 AM
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Smile

Carb bowl off - gas everywhere, at least with the engine cold. I am not confident this experiment would be safe with a hot engine. I suppose taking the carb apart and cleaning it would not do any harm. Something is causing vapor lock - can't see how it could be the coil. Perhaps I should add a fuel pump (only slightly kidding).

Thanks

Stefan
 
  #13  
Old 08-08-07, 05:21 PM
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I have chased lots of fuel problems and never found a "vapor lock" situation on power equipment. You can physically see the path the fuel needs to travel. Hard to foller them lectrons.

Its your time....
gl
 
  #14  
Old 08-08-07, 11:37 PM
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Ok, if after dumping the bowl, you still have a steady rate of fuel flow at the carb, then I believe either there is vapor lock occurring or a non-fuel related problem ( I'm sure this is a fuel related problem due to the fact that it will continue to run with full choke). Vapor lock usually is a rare occurrence outside of plugged gas cap vents. If you are confident that the amount of fuel flowing into the carb bowl is enough to keep it full while the engine is running, then I don't know what the problem is.

I've seen some that had fuel flow to the carb bowl, but it wasn't quite enough to keep up with the engine. After running the engine for some time, it would begin to die out. Partial choke usually helps it for a few seconds, and it requires more and more choke until it quits, or you stop and let the load off the engine so that it uses a bit less fuel, so that the bowl can become gradually fuller rather than gradually emptier. This sounds like what you're describing your mower to be doing. I think the rate of flow is marginally less than what is required by the engine when it is under full-load, but good enough to keep it running when not under a load.

>>>>Here's an afterthought: By any chance, are you having to jump start this engine? (bad battery)? If so, and if it has an electric PTO and a fuel shutoff solenoid on the carb, then the dead battery is the problem. The battery opens the fuel shutoff solenoid so the engine can run, the electric PTO drains the battery, until it is so low that the shutoff solenoid can't stay open and kills the engine. Shutting the blades off relieves the voltage drain so that the solenoid can hold properly (allowing the engine to run right again) with the current supplied by the alternator. It doesn't sound like this matches your description of the problem exactly, but close enough that it was worth mentioning.
 

Last edited by cheese; 04-19-08 at 12:53 AM.
  #15  
Old 08-09-07, 08:08 AM
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cheese I know you have multiple more years of experience on small engines than my mere 5 yrs. I still think the coil is worth investigating. At least to test the resistance from the primary lead to ground.
The one I posted about, I had chased for over a couple of seasons. I could continue to make it run with the choke or by adding fuel to the carb also and replaced fuel pump filter and chased fuel supply lines. I was never able to view a No spark condition until I simply restarted every single time then checked when it stalled. Then I only observed a very brief, (few seconds) of no spark.

Ok well I won't chime in again so.....

gl
 
  #16  
Old 08-09-07, 07:25 PM
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BFHFixit...Don't stop chiming in! You provide a lot of valuable input here, and it's appreciated. Same goes for all you other regulars who like to help figure out what's wrong with these durn broken small engines. (CAMINOKID, msidan, geogrubb, 30yeartech, smallengineguy, duigoose, etc...).

I have a lot of experience, but not as much as some folks, and I don't claim to know everything. I actually forgot your post about the coil when I stated I was sure this is a fuel problem. In fact I'm glad you re-stated it, because it's a strong possibility. A weak coil producing a weak spark could produce some or all of these symptoms. The more I think about it, the more I think it might just be the problem.
 
  #17  
Old 08-09-07, 07:47 PM
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heheh thx cheese, its easy to sit here n toss out suggestions when your not the one chasing gremlins.

I just checked the service manual for CV and CH 11-16 HP Kohler. This manual is 5.5mb and I aint got nuff room left to host it. But it can be downloaded at the kohler site http://www.kohlerplus.com/login.asp (thx 30yr) using Internet Explorer only. Enter as guest and you can navigate to your engine type, and find the manuals available. There is also a search engine.

The manual states under troubleshooting section,
Engine runs but misfires-
5. Faulty ignition coil

8.1 of the electrical section is a test for the module.
Measure resistance from the lamination stack to the high tension lead, (spark plug lead) Reading of the secondary should be between 7,900 ohms to 18,400ohms. If outside this range the secondary is either shorted (low or 0 ohms) or open (high or infinity)

This is not out of the kohler manual but it is in several lycoming and continental manuals-
If it tests good cold, you can also put it an oven at 150 degrees for 30 to 60 mins and test again.
 
  #18  
Old 08-10-07, 08:42 AM
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I can get the coil for $40.00. Assuming my time is worth anything, I may as well just replace it.

I'll report back.

Thanks for all of your help

Stefan
 
  #19  
Old 08-10-07, 03:03 PM
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I was not able to pick up a coil on the way home today, but nonetheless had to cut the grass. At only 64F, the motor did just fine, not so much as a hicup. Does that in any way affect your diagnoses? I dont want to replace perfectly good parts with perfectly new parts - at least with cars, that can get expensive.

Thanks again

Stefan

BTW all of your help is very much appreciated. I just did not (and still don't) understand how a bad coil can cause the fuel starvation in the filter.
 
  #20  
Old 08-10-07, 04:25 PM
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It's hard to judge the performance of a fuel system just by watching the fuel level in the filter. I've seen lots of them run all day with just a tad of gas in the filter. It doesn't really indicate anything. Now, if the filter goes completely empty, and you are not seeing any fuel flow into it, that's a problem.
 
  #21  
Old 08-15-07, 09:25 PM
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Heat creates resistance in electrical components. So yes that would support my diagnoses.
You can test it without replacing it using an ohm meter as I posted.
 
  #22  
Old 08-16-07, 06:08 AM
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That makes sense. Will do and report back.

Thanks again

Stefan
 
  #23  
Old 04-18-08, 05:53 PM
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update

Although it has been some time, here is an update. I bought a coil and installed it. The engine starts, runs, and idles like a charm, burns no oil and sounds strong. However, it still stalls under load, but will now immediately recover if I shut off the deck or stop moving. Somehow load on the engine makes it stall and sputter. I checked and cleaned all electrical connections, and found some rust on the ignition switch. The volt meter reads just shy of 14 volts with the engine at idle, tough to check it under load. I cannot locate any kind of fuel cutoff solenoid, and have already bypassed the seat switch. Any suggestions?

Thanks so much.

Stefan
 
  #24  
Old 04-19-08, 01:04 AM
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Hmmm.....

<scratching head>

I wish I could visually observe the rate of flow from the tank through the carb. I still suspect a fuel problem. I suppose you could easily and cheaply replace the fuel line from the tank to the carb to make certain that there isn't an internally collapsed hose. The inner hose of the fuel line can swell up over time and reduce the flow. The STX38 hasn't been made for quite a while now, so the line is old enough to exhibit this problem. If you do this, also note the fuel outlet nipple on the tank when you have the line off. Verify that there isn't anything stuck in it. I once ran into this problem on a mower and found something like the filter from a cigarrette butt in the fuel tank outlet. It ran fine until you loaded the engine, then it would sometimes cut out immediately, other times it took a few minutes.
 
  #25  
Old 04-19-08, 05:00 AM
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I replaced the fuel line last fall, did not however, put in a new manual cutoff switch. Since the ignition switch is only $12.00, I will put in one of those today, a new seat switch, and a fuel cutoff.

My last resort is to take it to a shop.

Stefan
 
  #26  
Old 04-19-08, 08:04 AM
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If you hook up your volt meter on the battery terminals and run the engine at full throttle and engage the deck you should still be getting better than 12 volts output. I do not feel that your voltage output will pull down this engine since it is a solid state mag. I still feel that you have a problem with your fuel pickup in the tank and are not getting enough flow for the high speed need for the engine making it run on the lean side and stalling.
 
  #27  
Old 04-19-08, 11:31 AM
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I took the carb off today, soaked it is gumout and blew out all crevices with compressed air. I also checked fuel drain at the carb and it flows full and steady (hot or cold). Problem persists.

Stefan
 
  #28  
Old 04-20-08, 06:40 PM
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Because I cannot leave well enough alone, I removed the carb once more today, and used some wire to clean out all the jets and passages. Upon reinstalling, fuel shot out of the muffler the first 10 seconds it tried to run, then it ran great for 30 seconds, and then died from idle. It will now only run for 30 seconds, load or no load. The fuel fountain scared me. I have now either broken the carb for good, or blown the engine

Time to take it to a shop?

Stefan
 
  #29  
Old 04-20-08, 11:33 PM
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Sounds like the float stuck, or needle isn't/wasn't sealing for some reason. Does it still shoot fuel out the exhaust when you start it? Seems like we went from not getting enough gas to getting too much. Makes me think there is a problem in the float/needle area. If the needle doesn't open far enough, it would starve the engine like it was doing, and if the needle doesn't close, it will flood the engine like you just now experienced. Does the bowl have any dented in spots on it?
 
  #30  
Old 04-21-08, 07:42 AM
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No, the bowl seems fine. It no longer shoots fuel, but now it won't stay running, even at idle. New carb is about $90, which is the same as having it picked up and looked at (without any work being done to it). I don't mind spending another $100, but at some point the money would be better spent on a new mower. After all, this thing is about 20 years old. I wish I were not attached to it.

Thanks
Stefan
 
  #31  
Old 04-21-08, 05:32 PM
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I went ahead and bought the carb. At first, I thought is was the wrong one as it had a cut-off solenoid which the existing one doesn't. Turns out, someone had removed it - the connector was still there and showed 12v with the ignition on. So, new carb on, hooked up, engine starts, grass gets cut, no bogging, sputtering, stalling.

It was fuel related after all. Although it cost me about $75 in unnecessary parts, the problem seems to have been fixed. Thanks to all for reading and helping.

Stefan
 
  #32  
Old 04-21-08, 10:33 PM
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Whew!

Glad to know that solved it. We got it narrowed to a fuel problem, but sometimes without being there to observe and check in person it's hard to pinpoint a problem with nothing other than text. This one was beginning to cause grey hairs, lol!
 
  #33  
Old 08-30-08, 09:48 AM
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Similar issue!!

Hi,

I don't know if this thread is monitored anymore, but I'll give it a shot.

I have a JD STX38 (black deck) with a Kohler Command 13hp engine. Originally, my problem was the same as that desribed in the beginning of this thread. That is, it would sputter, spit, etc., when a "load" was placed on the mower. I just installed a new carb and things have gone from bad to worse. Here's what is happening now:

It starts fine and idles well. If I leave it in neutral and release the brake it dies even without the PTO engaged. If I give it full throttle and release the brake it might stay alive, but if I engage the blades or try to drive it forward it dies. I can always recover before it dies by pushing the brake pedal back down.

I can do everything with it in Reverse. I can release the brake pedal, drive it backwards, and cut the grass and it runs as smooth as silk no matter what the "load" is.

Does anyone have any idea what might be causing this? I'm willing to try anything, but I don't want to spend too much more money on this old beast.

Thanks in advance for your help.

Tom
 
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