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Kohler Magnum and loss of power.

Discussion in 'Mechanic and Repair' started by mdgil, Jul 26, 2007.

  1. mdgil

    mdgil LawnSite Member
    Messages: 5

    I have a M18 Kohler Magnum (Spec# 24608 ) on a Grasshopper 718K.

    The mower sat for a while. Before it sat up it worked pretty good.
    When I went to see how it would run - it sputtered and the governor would hunt and would backfire. I performed a quick cleaning on the carb ( it was gummed up) and I replaced the air filter, spark plugs, and the gas and gas filter, I even replaced the old line with new line.

    It runs much better now and hardly hunts anymore but I am not getting any power from the mower when I engage the blades or try to move. If I do both the engine sounds like it will die. O.K.

    I now re-cleaned the carb (fully cleaned -- 3 day acetone dip and used a carb kit), I cleaned the carbon off of the heads, valves and pistons. I lapped the valves/seats with compound and a hand lapping tool , they are now all with in lash specs, Replaced the intake valve seals (none on exhaust), cleaned the intake manifold, I also replaced the breather filter and breather/valve cover with that little 'flapper valve'. I bought a gasket kit and replaced all of the gaskets that I took off. I torqued down everything to specs. Adjusted the carb to initial specs and reposed the oil and filter to correct level.

    It will now start up great and it no longer backfires or governor hunts. I am still having power loss engaging the blades or trying to move. I even took the deck off and just 'rode the mower' and the power was cut by 1/4 the power or more. (it would seem - no way to know exact power loss #s).
    This is better than before but the power loss problem is the same. I also want to state that before one cylinder would get very hot and after the tear-down it still gets very hot. (example: I can barely touch the exhaust bolt on cylinder side #2 [left side facing flywheel] -- on Cylinder # 1 I can touch it for a few seconds). I have no idea if it is normal for one cylinder to be that much hotter that the other. I did a compression test and I get around 95 psi for both cylinders (one 95/96 the other was 94/93). I think this is low but I did one a couple of years ago (right before Hurricane Katrina Aug '05)and it was only slightly higher and ran strong. I am thinking about getting a leak down tester at Harbor Freight tools and see what that tells me but I am at a loss here. In-line spark tester shows spark (I don't know how to test the quality of the spark)

    oh also since this is a twin and I read some post about removing the plug to see if it was running on one cylinder. It I remove either plug the engine will die. The post were on newer engines so I do not know if it pertained to the Kohler magnum twins or not.

    One last thing, the reason it sat was because Hurricane Katrina tore my shed apart and a limb fell across on top of the air cleaner. It bent the air cleaner assembly and that was replaced and the intake manifold 'appears' to be good and flat when I cleaned it. It it was a hail line crack that I could not see... would it cause me problems?

    Sorry for the LONG post but I know you guy like to know the facts and figures so you can post a more accurate response.

    1. One cylinder/side is much hotter than the other. Normal?
    2. Starts good and runs until you put a load on it.

    Thank for any help that you can offer. I can get what ever information that you need (unless I don't know how). :confused:
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Is this in-line spark tester you are using a neon or light type ? These will give false test on some engines, Kohler has their own tester that looks like a spark plug.

    Given the fact that you have a hotter cylinder than the other leads me to believe the colder cylinder is not operating (Possibly spark ?). Remove both plug wires and put a phillips screw driver in each. One at a time and hold the screw driver about 1/8" from a ground surface then crank the engine over. You should see a nice dark blue spark jump to ground.

    If you don't get a spark or it's orange/yellow in color disconnect the white kill wire coming out of the blower housing with the plug wires and test again.

    If there is no change the coil (module) is most likely bad.
  3. mdgil

    mdgil LawnSite Member
    Messages: 5

    Yes it is a in-line spark tester with the bulb. (prime line).

    Hmmm.... funny thing happened. After I posted I went out and I never adjusted the low idle stop screw (not idle mix screw). {to adjust the idle when I throw the throttle all the way down}. So I adjusted the idle speed.

    I then took off a spark plug lead (cooler cylinder) and it kept running! I took off the plug on the hot side (other side re-connected) and it died. It only does this at low idle. Any speed higher and any plug disconnection will kill the motor. Good this is finally something that I can recreate and narrow down.

    I did you suggestion and both plugs will fire about a 4mm (guess) line of a violet/purple colored spark. Now here is the funny/weird part. One the hot cylinder it not run with the plug off and I needed a helper to crank the engine due to the seat safety switch BUT the engine will run with the cooler cylinder unplugged only at low idle. IF I put the screwdriver to any ground point and increase the RPM it would run (still bad but run at increased RPM).

    Let me clarify.. I unplug the plug wire and put the screwdriver in it and place ground (or allow the spark to jump) to ANY ground point the mower will stay running even at a higher RPM. The second I remove the screwdriver away from a ground point the mower will die (if it is running at a higher RPM). The hot side would not do this and would backfire when I tried to run it with the screwdriver to ground.

    I removed the plugs and the colder cylinder was wet with gas and the other was normal. I cleaned off the threads and electrodes and re-checked the gap. All looks good.

    I am thinking that maybe the new spark plug is defective or cracked but I do not see any cracks. Hairline?

    I went out to look again for a crack before I submitted this post and decided to swap the spark plugs with each other. It is working great now!!! :cool2:
    I engaged the blades and the engine no longer bogs down! I am ordering six new plugs to keep some extra on hand. I am guessing that the spark plug was grounding to the block. It is working now but it may still be cracked/defective. Both cylinders get equally hot now.

    Phew!! I have been cutting two acres with a push mower for over a year (Hurricane Katrina insurance B/S and rebuilding occupied most of my spare time so this was not a priority). I missed the most important rule --> KISS (keep it simple stupid). Ah well... The block did not get de-carboned and valves were not cleaned and adjusted in about 4 years so it needed it anyway.

    Thank you Restrorob (you were on the money with electrical) and Mowingman (for the specs and trans information) for your help. It is greatly appreciated and people like you make the world a little better. :)

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