View Full Version : missing lack of power fouling one plug Kohler

04-18-2007, 09:55 PM
I have a Kohler, model number CV740S 2004 twin cylinder vertical shaft that is fouling the left plug, black soot, misses, when you shut it off it back fires. Performed a cylinder leak down test when air put into the suspected bad head, I can hear air coming out of opposite head and crank case. Compression test I have 165PSI both cylinders was told possible cracked head.

Does anyone else have any suggestions or believe that this diagnose is true.


04-18-2007, 10:26 PM
Head gasket

04-18-2007, 10:29 PM
Did you use a leak-down tester or just plug a air hose up with 120 lbs. of air ?
Where exactly is the air coming from on the other cylinder ? (head gasket area, intake or exhaust)

If it were a head gasket the plug would be wet and oily or you would have a oil leak in the gasket area on the outside.

Sounds to me you have a coil thats not firing or firing weak. Have you tried another spark plug ?

04-19-2007, 10:44 PM
i used a leak tester at 30 psi and 80 psi left cyclinder ,the air comes out the ather cyclinder,by the sound comes from the area of the push rods and rockers.i have put a new coil and new plugs no fix

04-19-2007, 10:58 PM
thankyou for your help i am new to this site.i have worked for gm for 20 years
the cars are easier.the leakage is from the ather cyclinder at any psi. with
a leak down tester. the plug is black sooted dry after 5 min of operation.no leakage found around head,what about the spark advace module that goes to the coils. thank you for your assistance i am stumped!!!!

04-20-2007, 12:17 AM
did you take the head off?

04-20-2007, 10:17 PM
not yet thanks i will let you no thanks,i still am thinking about that moduel on the side

04-20-2007, 11:53 PM
Below is the only test the average person can perform on the SAM module. Other testing requires a special tester. Make sure you have at-least 7.5 volts on the red main feed wire going into the SAM in run and start positions. REMOVE the black ground wire coming out of it and check for corrosion on the connector and screw. Also check BOTH coils at the wire connectors AND mounting screws for corrosion.


Bill Kapaun
04-21-2007, 01:11 AM
"the air comes out the ather cyclinder,by the sound comes from the area of the push rods and rockers."
That's typically where the head gaskets blow.
There is only a very thin gasket area between the cylinder and the push rod galley.

Here's a link to the service manual if you don't have it-


04-21-2007, 01:05 PM

When a leak-down test is performed a certain amount of air passes the rings into the crankcase. Once the crankcase is full of air a certain amount of air will bleed out through the breather system and the oil return passages in the head.

This would account for hearing air around the push-rod area on the opposite cylinder being tested.

04-22-2007, 09:52 PM
thankyou for all your help i will test the moduel tomarrow the pull the head
if the moduel is good.then i will let you all know what i find thanks

04-24-2007, 01:07 PM
I have a '94 Bunton with a Kohler Command 25hp horizontal shaft engine that I acquired last year. The previous owner mentioned that the mower tends to backfire when not under load; from what I can tell, he "remedied" this by adjusting the choke to get it to stop backfiring.

This spring when I went to start it up, I pulled the plugs and the plug on one cylinder was COMPLETELY fouled. I cleaned it off and it started right up, but I can't help but wonder if the two problems are related. Any advice on what to check? The hour meter on the mower reads 930 hours.

Is the backfiring likely related to some carb issues? What would cause one side of the engine to foul while the other seems to burn cleanly? I haven't noticed any smoke, but it does seem to consume oil. Can you do a compression test on this motor, or do you need to have a leakdown test kit to accurately diagnose if I have a cylinder/valve problem?



04-24-2007, 06:26 PM
i have not pulled mine apart yet i tested the moduel and it works i have looked athe the choke and is ok when i pull the head off i will let you no what i find. did you check the coil, just switch them and run see if gos to ather side

06-15-2007, 05:22 PM
i have a kohler command that is fouling the left plug,runs rough and smokes tryed coil swapping,tested the moduel per service manual,compression test good cylinder balance test had i thought bleed down.i pulled head put water in it no leaking down the valves.cant see a cracked in the head.should i send head out t6o have magna fluxed and valve checked.i am stymied:hammerhead: module#cv740s
family 4khxs 7252gc
spec# cv740-0024 any help?

06-15-2007, 07:17 PM
First, These head gaskets will not necessarily blow out like a auto head gasket. Sometimes you can't see any sign of being blown.

Look down in the lifter valley, You will see a small screw holding a little gold bent looking piece of flat bar. This is the crankcase breather reed assembly, Remove the reed and check it for wear and flatness then check the round port for any burrs that may keep this reed from laying flat. If this reed does not seal it would cause the same symptoms you are seeing.

I never go into a suspected blown gasket engine without replacing this reed, it's only a couple bux then you have piece of mind this will not cause a future problem any time soon.

Also check the head for flatness.

06-18-2007, 09:03 AM
I have the same problem on a 22 hp Kohler ; exmark 60 . THe left side , as you look from the handlebars ,has been fouling the plug every 4? days , now doing it once a day . This machine is also using a considerable amount of oil . I've been keeping it alive by rotating through about half a dozen plugs that I blast clean at home . 2,650 hours ; does it owe me anything ? Anyone have luck with rebuilt engines , and what did that cost you ?