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I bought an old riding lawn mower (B&S 12HP). To start it, I had to jump it from a car. The battery also looked old, so I replaced it with a new one. When I tried to start it with the new battery, all I got was a little half-turn sound from the engine, and then nothing. Subsequent attempts yielded nothing.

I assumed that since I had been able to jump the mower from a car, all I should need would be a new battery.

I tested the old battery's voltage with a multimeter and got 5V. I tested the new one and got 12V. That's the limit of my diagnostic skills.

Any suggestions for what to look at next?

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1 Answer 1

Attach your voltmeter to the battery. While the starter is trying to turn check the voltage reading. It should be between 9.5 and 10volts while cranking. If the reading is lower either the starter is bad or one of the battery connections is loose corroded. If it has an external solenoid/relay it may be the problem also. The solenoid will be a relay mounted to the frame, verify that it is bolted securely as it requires a good frame ground. The positive battery cable attaches to one side and a similar cable goes from the relay to the starter. You can trouble shoot the solenoid by attaching an automotive jumper cable from one terminal on the relay to the other. Wear eye protection and be prepared for some sparks. If the starter spins normally the relay is the problem.

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+1, I'm betting on corroded contacts somewhere (which lower effective voltage), and/or a bad relay. –  Nick Sep 29 '12 at 21:31
    
I asked my neighbor to help me diagnose the issue. While he was standing there, it started up just fine. Sorry I don't have a more definitive conclusion. It's been working OK for the last few weeks. Thanks for your suggestions! –  Jeremy Stein Oct 16 '12 at 16:04
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