# Kohler CH25S engine low idle problem



## jetblue4400

I have a Simplicity Legacy 1997 with a Kohler CH25S engine with a Keihin 24-053 34 single barrel carb.The engine specs are 1800Rpm at Idle and 3600Rpm Hi speed.I have a intermittent problem with the Idle.It seems to miss at times at low idle but runs great at full speed 3600Rpm under a load (Blades turning).The ignition modules and speed advanced module were changed last year for a different problem and did not have this problem then. Compression on both cyl is 110Psi.Changed plugs ,I have taken the carb apart and removed the low speed jet and cleaned that and the entire carb.The fuel sol mounted on the carb is working fine and ran a external tank with fuel directly to the carb to try and eliminate the fuel pump and still the same problem.There is only a low speed fuel idle screw on the carb and that does not seem to make a difference in adjusting the problem out.The adjustment does work in adjusting the idle but not eliminating the miss. I have to think its a fuel problem because under a load at higher rpm it runs great.The only thing I have not done is get a carb kit .Usually that only contains the gaskets and a float needle but I may have to do that. Has anyone got any thoughts?

Thanks


----------



## Country Boy

Did the problem show up after the ignition system was changed, or is this something more recent? Its possible you got bad parts. Also, check the connections on the Smart Spark system and make sure they are absolutely clean. I had some running issues with a Kohler at the shop that ended up being a dirty/corroded connection at the Smark Spark module. The system is very sensitive to voltage changes, and a bad battery or voltage regulator, or dirty connections can vary the voltage beyond its specs. That was recommended to me by our parts distributor for Kohler at work.

Does the unit surge at all when idling or running full throttle without a load? If so, I'd suspect a blockage in the idle circuit in the carb. The engine runs mainly off the idle circuit even at full throttle if there is no load on the system. Once you apply a load, the throttle plate starts to open and it draws more and more from the main jet and less from the idle jet. If possible, I'd remove the carb and disassemble it, then soak it in a carb cleaner (I use Hydro Seal II) for several hours. Once out, flush it with spray carb cleaner and blow air through all the ports and passageways. Reassemble with a new gasket set, and probably a new needle (just to avoid problems in the future) and re-test unit. If that doesn't help, then the problem is either not spark related, or the carb is beyond repair.


----------



## jetblue4400

*Pulled engine*

After running the tractor for about a hour up and down a hill with the blades turning the rpm's went from 3400 to around 1200rpm.I drove the tractor into the building and turned the lights off and looked at the spark on both cyl's with a spark indicator and on cyl #2 I had no spark.Cyl # 1 was fine. I checked the resistance of the ignition coil on #2 cyl from anode lead to ground and it measured around 10K ohms which is normal for the secondary coil but could not check the primary leads because they are behind the flywheel. Well to make a long story short I removed the engine and cover from the flywheel and ordered both ignition coils and sam module.The sam module has two outputs one for each drive signal to the primary coils of ignition coil 1 and 2.I have a kohler sam module tester and the module did check out good as well as both ignition coils both primary and secondary resistance checks,but I can't take a chance on any one of these ignition coils and sam module heating up and causing the same problem again as long as I have the engine removed.last fall I replaced both the coils and sam module because I had a similar problem and one of the coils was open between the anode lead and ground,so I had to pull the engine to change it, so I replaced all three units.The plugs look good ,compression is 160 and 170 Psi and hooking a timing light up showed me the sam module was advancing the timing and working. The parts will be in this coming week. $$66.00 for both coils and $57.00 for the sam module. I must say with both coils checking good with a resistance check and the sam module checking good with a sam module checker, I'am not sure after installing these 3 parts and reinstalling the engine that the problem won't show up again.I purchased this Simplicity legacy tractor for $1300.00 .Its a 1997 with 1300 hours on it and I rebuild everything except the engine.I have about $1800.00 of extra parts in addition to the $1300.00 so I'am in a position where I can't turn back and stop.I know the dealer where it was originally purchased and he told me the tractor with a snow blade which I have was close to $10k when new.


----------



## jetblue4400

*Fixed the problem*

The parts came in the other day 2 ignition coils and 1 sam module and I replaced all three units ,installed the engine and fired it up.I just completed mowing 2 acre's and no misses from the engine and no boging down .Rpm's stayed up at 3400 full load all of the mowing time.Both the coils and sam module checked good out of circuit with a ohm meter for the coils and a kohler sam checker for the sam module.I still don't have a firm answer at this time if I cured the problem, Only time will tell. There is a possibility that when the coil gets warm it breaks down which may have caused the problem. After spending another a $130.00 on the same parts and removing the engine I hope I have the problem solved.What I have determined is that when the problem was happening (missing) and If I pulled the anode lead off of one plug and used a spark tester to ground , the engine ran on the other cyl and did not miss a beat ,but when I performed the same test on the cyl that i thought was bad the engine would not run .Now when I installed the second set of coils and sam module I did the same check and now both cyl will run when performing that test. That test also proved that there was no problem with the carb because it ran fine on one cyl.
I will post again if the problem comes back.


----------

