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Kohler command


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#1 caseguy OFFLINE  

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Posted October 01, 2010 - 07:22 PM

Afriend of mine has a 2000 WH 312-8 with a 12.5 HP Kohler Command engine. It runs really well for about 1/2 hour and then starts to miss a little. It will run like that for another 10 minutes and then it starts to miss horribly! At first it seemed as though choking it would allow it to run a little better but once it starts missing really bad, that no longer affects it at all. Another thing that happened, and may be a coincidence, is that when it is running crappy, playing with the spark plug wire affects the way it run a little. However when it's running well it doesn't cause any change. Every once in a while by playing with the throttle and the choke, we'd get it to run pretty good, but upon throttling up, it would start missing again. My first instinct says it's a carb problem or a fuel problem of some sort. What does everyone else think?

#2 DH1 OFFLINE  

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Posted October 01, 2010 - 07:45 PM

First thing I'd do is put in a new spark plug.

#3 caseguy OFFLINE  

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Posted October 01, 2010 - 09:05 PM

Definitely worth a try. Thanks.

#4 MH81 ONLINE  

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Posted October 01, 2010 - 11:32 PM

Is it a "Champion"? :D

Another thought... is that a mag or a coil? If the cooling fins are all clogged up, could something be breaking down due to over-heat?

#5 caseguy OFFLINE  

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Posted October 02, 2010 - 10:32 PM

Another day spent wrestling this horse! I changed the fuel filter (because I thought it remiss that I hadn't done so earlier). I put a new spark plug in, gapped to factory specs. I COMPLETELY disassembled and cleaned the carb. It ran like a champ...for about a half hour. I did try and make some observations while it was running poorly though. It seems to be running very rich (raw gas in the exhaust) when it starts acting up. I can't help but think at this point that it's the pick up coil, or "ignition module" as Toro calls it (BTW, it's a $60 part AND it's 3 days away in some warehouse somewhere). I will take my inline spark tester with me when I next go over and see if the spark is erratic or weak when it begins to miss. Someone suggested valves sticking, but I don't think it'd run rich with either of the valves stuck open, but IDK, I'm not an expert and I've never experienced sticking valves in person. I will also take my compression tester with me next time and do some cold / hot readings. Any opinions or suggestions are welcome. I just hate using parts to troubleshoot!

#6 DH1 OFFLINE  

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Posted October 03, 2010 - 07:05 AM

Did you check to see if the cooling fins are clean and free of debris? That would be my next guess.

#7 caseguy OFFLINE  

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Posted October 03, 2010 - 07:58 AM

They are clean and free of debris. The only issue that might cause overheating is a broken exhaust gasket that is allowing exhaust gases to blow onto the fins, but in a limited area only. I'll have to get the gasket on Monday. Was on my to do list anyhow.

#8 MH81 ONLINE  

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Posted October 03, 2010 - 08:00 AM

...I just hate using parts to troubleshoot!


I mulled this over last night, and came up with all the same thoughts you already have... as for the parts, I run into this at work all the time. I feel guilty "trying" parts as someone has to pay for them, but my boss put it in perspective for me. "The customer wouldn't have called you if they didn't trust you. Troubleshoot as best you can, but at some point, you have to act on your best guess."

After you do the tests you mentioned above, (no lower compression after hot, spark shows erratic) your just gonna have to explain why your best guess is going to cost them $60, but make sure they know you're changing this cause you've eliminated the rest as best you can without ripping the head off.

Also, what are you charging this guy hourly... Nothing right? Maybe a lunch and a tip if you do get it running...could be time to Hail Mary and hope.

#9 DH1 OFFLINE  

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Posted October 03, 2010 - 10:18 AM

Well you got a new spark plug, clean cooling fins, clean carb. and it still acts up, check fuel supply to carb. gas cap not venting or fuel pump if you have it. Small exhaust leak probably makes no difference.
If all is good and compression when hot the same there's not much else except ignition breaking down when hot.
Erratic spark when hot as mentioned above pins it down.

#10 caseguy OFFLINE  

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Posted October 06, 2010 - 11:25 PM

Just an update. I did the cold compression test...but it was useless for 2 reasons. 1) I couldn't get it to run long enough to get warm, and 2) I did some follow up reading only to discover that this particular engine has an ACR (automatic compression relief) system on it. Any time the engine spins at less than 700 RPM (cranking speeds) the ACR opens the exhaust valve a little at the start of the compression stroke reducing the compression to about 2:1. I did however talk to a local mechanic who said that the aluminum heads with overhead valves tend to loosen the exhaust seat inserts fairly easily under adverse running conditions...like detonation. I also believe that the bad exhaust gasket may have had more to do with this than I originally thought. I talked to a friend who said that the aluminum heads SHOULD NOT be run with a compromised exhaust system as it may "burn out" (his words) the exhaust valve seat. That's where I'm headed next. I'm just glad that it's not peak mowing season!

#11 tyler OFFLINE  

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Posted October 07, 2010 - 05:06 AM

just got done a rebuild on my onan 16 twin. yesterday fired her up, it was hard to start, but when running it would only run with the choke on. i screwed around with needle screws for over 2 hours and got it running ok. but something was wrong, so out came the small engine books. make a long story short i had the needle screws in the wrong holes. runs like a dream now

#12 NUTNDUN OFFLINE  

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Posted October 07, 2010 - 02:28 PM

Caseguy, can you try a different spark plug wire? I know it sounds odd but just like the coil once it gets warm everything expands and could be causing a very minor break in the wire to pull apart. Plus it would be easier to replace the wire then start digging elsewhere.

#13 caseguy OFFLINE  

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Posted October 07, 2010 - 02:38 PM

Caseguy, can you try a different spark plug wire? I know it sounds odd but just like the coil once it gets warm everything expands and could be causing a very minor break in the wire to pull apart. Plus it would be easier to replace the wire then start digging elsewhere.


Well I finally found it. You're right on the money George. In the end it did turn out to be the coil or the wire. It's impossible to know for sure which because they're integral to one another. I got it running and when it warmed up it started acting up again. I quickly threw the spark tester on it and sure enough, the spark was intermittent. But just to be sure, I tested the coil with a meter, following the manuals instructions, and it was bad! Got one on order and there's an off chance that it'll be here tomorrow, but more likely on Monday. I'm just glad that it's figured out. It's really been nagging at me. Thanks to all of you for your suggestions and your support! I will add a last (I hope) post when I get the coil installed.

#14 NUTNDUN OFFLINE  

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Posted October 07, 2010 - 02:44 PM

Good deal. I am glad to hear you got it figured out. Please do let us know how she runs once you get the new coil and wire in place. :D

#15 caseguy OFFLINE  

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Posted October 09, 2010 - 02:31 PM

I received the coil and installed it this morning. It runs great! In addition to the coil, I installed a new spark plug, a new shut-off valve/strainer, flushed the fuel tank, thoroughly cleaned the carb, cleaned out what debris there was on the cooling fins, replaced the left front tire, re-welded the heat shield brackets onto the muffler, replaced the bad exhaust gasket, and repaired the leaky oil drain tube. Now it looks better and had a pretty thorough tune-up to boot. Hopefully it will serve him well for many years to come.




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