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2025/01/17 22:14:51
Batdevice

Trouble with a Kohler CH 760-3051 engine

Hi,
 
I have a Kohler CH750 30 hp engine that is giving me issues.  The engine starts and runs great. However, after warming up the engine and opening the throttle wide open the engine starts surging or it may start to belch out lots of heavy grey smoke and appear to run on only one cylinder. I figured it needed new spark plugs and replaced them.  Engine still did the same thing.   I then thought there may be a head gasket issue as the engine oil had gas in it.  I replaced the oil and installed a new head gasket on the cylinder that happen to have a black oily coating on one side of the cylinder head.  After removing the head there was a gas/oil mix laying in the cylinder.  The valves, piston and cylinder walls were good.  I would have bet money that that was what was wrong.  However, after installing the head gasket the engine did the same thing.
I assumed that one of the coils was bad.  Replaced both to the new Kohler 2 wire kit and this did not fix the problem.  I also removed the flywheel to see if the key was sheared or damaged which it wasn't. I replaced the other head gaskets and checked the valves for leaks, no problem.  I removed the fuel shut off solenoid to test it - worked as it should.  No change on the operation.  Figured that maybe the engine was either starved for fuel or was overfueling.  Opened the gas cap on the tank, cleaned the fuel sump supply line and removed the filter to no avail.  When revving the engine it will sometimes burp up oil/gas solution and blow it out the air throat in a spray.  Almost like a backfire.  I am stumped as to what the issue is with this motor.  Any help would be greatly appreciated.   
16 comments Leave a comment
SRTsFZ6
Start the engine (mid throttle) and pull one spark wire off at a time (carefully). 
 
You SHOULD hear / see the engine RPMs drop IF THAT CYLINDER IS WORKING.
 
You should also ground each spark plug to the head and look for actual spark.
 
Re-reading your post, I would inspect the carb closely.  Sounds like one side is possibly flowing too much fuel.
I believe that engine has two main jets inside it for each cylinder.  It's possible one jet vibrated out causing 
the issue to one side of the engine..
 
 
Plz post back what you find...
 
 
 
.
2025/01/18 06:50:22
SRTsFZ6
Page 25:
 
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://resources.kohler....24_690_06_EN.pdf    
 
(Copy, paste-search)
 
.
2025/01/18 07:00:07
Mikel1
Since there was gas in the oil, carb needs to be cleaned. If the level is high in crankcase then it will spray out the breather hose to carb and air filter
2025/01/18 10:54:42
Batdevice
I checked the oil since yesterday and it is at the full level.  Removed the carb and blew out the orifices.  Reinstalled it and ran it.  Runs prefect at mid idle.  Speed it to high and it blows out grey smoke to choke you.  may even backfire a spew oil/gas out the air iinlet.  Seems to run on one cylinder only briefly.  I even thought that the cable from the battery may be an issue as it wore through to the frame.  put on a new one.  no change.  I am at the point of burning it.
2025/01/18 22:23:30
SRTsFZ6
Do at last a compression test on the engine.
 
Also, if the muffler has a spark arrestor(fine screen), pull it out and check for clogging from carbon build up  That clogged up can cause major running issues (limited RPMs), spit back into the carb as well.
 
I gather you checked valve clearances and inspected that the valves were visually opening fully/ the same..
 
.
2025/01/19 06:46:57
Batdevice
Hi again.  Thanks for the feedback.  I inspected the muffler and it does not have a spark arrester.  No difference running with or without the muffler actually.
I checked the valves and they appear to be moving the same amount of travel on both cylinders.  The minimum lift clearance is slightly greater than what is specified in the shop manual for both intake and exhaust.   I did notice that the fuel pump diaphragm was leaking gas into the #2 cylinder which would explain the gas in the oil.  I replaced this with a new pump/valve cover thinking that this could be causing the running issue but there is no change. 
I made a video of the way the engine works and posted it on you tube so you can see what it is doing.  Here is the link:
 
 
Thanks
2025/01/19 20:33:04
SRTsFZ6
From you as your post doesn't show, nor your link:
 
Hi again. Thanks for the feedback. I inspected the muffler and it does not have a spark arrester. No difference running with or without the muffler actually. I checked the valves and they appear to be moving the same amount of travel on both cylinders. The minimum lift clearance is slightly greater than what is specified in the shop manual for both intake and exhaust. I did notice that the fuel pump diaphragm was leaking gas into the #2 cylinder which would explain the gas in the oil. I replaced this with a new pump/valve cover thinking that this could be causing the running issue but there is no change. I made a video of the way the engine works and posted it on you tube so you can see what it is doing. Here is the link:
 
So you did replace the fuel pump-That's mechanical pump yes?
 
You REALLY need to do a compression test or better yet a "leak down" test...
Confirm the valves are NOT leaking.  You mentioned previously their ok- How'd you test them?
 
.
 
.
2025/01/19 20:48:05
Batdevice
Yes I forgot to mention that the compression was 180 lbs on both sides.  Yes the pump is mechanical. 
I hope the link is showing as a image.  This site does not allow me to post a link to your tube. 

 
2025/01/19 20:58:54
SRTsFZ6
Try PMing me with the link. 
 
You have to be on this site for awhile and then the moderator has to approve your post WITH A LINK..
 
Also, if you can pick up a spark tester such as this (cheap on Amazon) and verify your not loosing spark 
at higher RPMs:
 

 
.
2025/01/19 21:08:30
Mikel1
https://youtube.com/shorts/JjIBINIc4o0?feature=shared
2025/01/19 21:26:57
SRTsFZ6
That appears to be engine oil burning from the engine (in the exhaust).
The engine runs good-so I don't believe there's a fuel delivery issue
nor spark issue.  Something inside the combustion chamber is amiss. 
 
Are both plugs getting oily / fouled?
 
It also seems you get much more smoke when de-celling the engine, correct?
 
I'm leaning towards the oil rings being worn (I know you have good compression).
Worn valve seals / guides would cause smoking but more "steady".  
 
The back firing, running crappy, smoke is a result of excess oil in the combustion chamber.
 
Advise on the spark plugs..
 
..
2025/01/20 06:38:05
Batdevice
Yes both are fouled.
 
In the video I slowed down the engine at the time it started to surge because it will continually do so at full RPM and the shop would be full of smoke.
 
Thanks
2025/01/20 09:05:31
Batdevice
One more thing I forgot to mention.  I pulled the dipstick when the engine was running normally (when cold) and it started pushing out oil out of the tube.  As soon as I did that the surging started to be more pronounced and it was pushing out more smoke then before. 
 
2025/01/20 09:10:57
Mikel1
Yeah sounds like the rings since you replaced head gasket. Leak down tester would confirm
2025/01/20 09:46:18
SRTsFZ6
I gather if you pull the fill cap on the valve cover, you'll get lots of oil "vapor" coming out?
 
What your describing is piston ring blow by, IE the rings are worn out-allowing combustion gases
to push into the crankcase.  
 
As long as the cylinders are not scored up, no MAJOR wear to them, you can hone the cylinders and simply re-ring the pistons / engine...  
 
My 18 HP Brigg's (from my Toro zero turn). Had to replace the piston, rings and head 
as a valve seat let loose... Cylinder was fine, just a hone for the new rings to seat..
That was 5 years ago, doesn't burn a drop of oil (nor leak):
 
2025/01/20 09:53:56
Batdevice
Thank you gentlemen for the information. 
2025/01/20 20:06:00

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