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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 18995
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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PROBLEM Kohler (Command CV20) 20 hp engine on a Scag 48 in.

Resolved Question:

PROBLEM: Kohler (Command CV20) 20 hp engine on a Scag 48 in. mower. About a month ago the engine died while mowing for no apparent reason. The battery was weak so I had to jump start the engine. At that point of having 391 hours on the engine, I decided to replace the battery, spark plugs, and the fuel filter. Everything went fine until today. Again the engine died while mowing. The battery was too weak to turn the engine over. I jump started the engine and continued to mow. In about a minute while mowing the engine died again. I jumped it again. As soon I would engage the mower blades the engine would begin to die but disengaging could keep the engine running. Putting the engine under stress would cause the engine to die. There seems to be some electrical problem since the new battery gets discharged while the engine is running. HELP!
Submitted: 4 years ago.
Category: Small Engine
Expert:  Curtis B. replied 4 years ago.

curtis b :

You have an electric fuel shutoff solenoid in the base of the carburator. It has to have 12 volts to keep it open and the unit running. If the battery is not being charged, the voltage will get low and shut off the engine. The big load on the battery is the electric clutch for the blades. What needs to be done, is to repair the charging system, You have the coils mounted under the flywheel and the regulator (rectifier) mounted outside .

curtis b :

You should start by reading battery voltage with the unit off, 12.5 or more would be about right, then with engine running at full throttle voltage should be above 13 volts dc. iF NOT, THE CHARGING SYSTEM NEEDS TO BE CHECKED. To check the alternator coils, unplug thenm and with volt meter set on a/c volts, check the voltage , should be above 20 volts a/c. It alternator output is ok, check the recifier, voltage should be around 14 volts d/c.

curtis b :

Let me know, thanks.

Customer :

Curtis, I think somewhere in your answer is the solution. I will not be doing the checking until Friday since we are into Thanksgiving. I know that you have given me a detailed check list but I may call on you for more clarification when I do the checking. Thank you for your help so far. Jimmie

curtis b :

No problem. Jimmy, start with the battery check, 12.5 volts or more, while you are at it check the positive post to the frame, if the ground system is good it will read the same as battery voltage. Then check the battery voltage with the engine running it full throttle. That way you know if you need to go further. Thanks.

Customer :

Curtis,

Customer :

Curtis, the battery checked 12.01 with the engine off and 12.05 with the engine running. Checking later while the engine running was 11.89 and 11.88 with negative lead to the frame. I think I should replace the battery first before doing anything else, but it is only a month old.

curtis b :

The battery is just showing weak and it is not being charged. The charging system is the problem. I would not change the battery as it is only showing weak, a charger would bring it up easely. Check the output from the alternator and if it checks ok, check the regulator. Also when jumping a mower or any small engine with low amp alternator, never have other unit running. If you jump off of say a pickup, the alternator on the truck is putting out upwards of 60 amps into a 15 amp system. This burns out the small engine charging system.

Customer :

I have found and fixed the problem. When looking at the rectifier, I found the grounding strap that attaches to the engine to be loose. It had obviously heated up and even arced and etched the screw. I had to tighten it many turns to get it in full contact with the engine. The voltage is now 14.5 with the engine running. The battery was in warranty, so I replaced it. Everything seems to be working fine. Thank you, Jimmie.

curtis b :

Good job!! Thank you.

Curtis B., Technician
Category: Small Engine
Satisfied Customers: 18995
Experience: have worked on and around most engine models for 35 yrs./Polaris ATV expert
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Curtis B.
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have worked on and around most engine models for 35 yrs./Polaris ATV expert