Craftsman tractor won't start (yeah, heard that one before!)

Hello, I'm pretty much an idiot when it comes to small engine issues, but I want to learn, so I am trying my hand here.

I have a Craftsman lawn tractor; it has a B&S 20 ohv engine, model 331777. I have had no issues for probably 8 years or so. Last year I ran over a stump and ended up having to replace the fly-wheel key.Completely unrelated to the current issue, but I wanted to mention it.

A couple of weeks I was mowing the first time this season. Just as I was finishing up the yard the engine started sputtering, as if the gas was low, and eventually cut off. I ended up pushing it into the garage and didn't really think much about it for a couple of days since I had finished with the grass. I tried starting it later, and it would spin, but never catch and start up. Fast forward to yesterday, and I figured I might as well change the air filter, oil, and oil filter since it had not been serviced in a while. I also cleaned the spark plug. For some reason I didn't try cranking it until all that was done, and the engine would not turn at all. No clicking, nothing. My brother-in-law tested the battery, and it was dead. I'm not sure how likely that the battery would die 'that much' in two weeks, but the meter didn't lie, assuming he tested it correctly.

I went and got a new battery this evening. Both are U1 batteries; I have no idea if this is an issue, but the old battery had the poles at the top (if looking down from the top). The new one the poles are closer to the bottom. Positive on the left at all, so I know that part is fine. (I just think back to an old Honda Civic I had that needed a reverse polarity battery and always wonder about terminal placement!)

Anyway, I wanted to check here. I don't want this to turn into buying part after part, spending $20 here and $40 there, and eventually it being something major and, looking back, would have just been easier getting a new tractor.

OK I read this and I am not sure what you are asking. Can you give me the question in one or 2 sentences?

When mowers just stop & get pushed back people tend to forget to turn them off.
The solenoid on the carb ( and some new voltage regulators ) draw a small amount of power and can not only flatten a battery but kill it completely.

After that I did this while back

Before you start, pull the spark plug & try to rotate the engine by hand.
No use checking the electrics if you have a hydraulic lock, seized engine or jambed belt overloading the stater motor.
Assuming the engine turns freely.

I like to start from the starter motor and go backwards .
Do the following 5 tests, regardless of the results from an or all of them as there can be more than one problem and you want to isolate where the problem lies.
Elimination of individual parts is important so you know by the end, the battery, solenoid & heavy power circuits are all in good order.

1) try to jump the starter motor directly from your car or truck.
Starter turns = starter good

2) do the same directly from the mowers battery
Starter turns = mower battery good
No turn = duff battery, recharge it & try again.

3) check for voltage ( + 12V ) at the solenoid trigger wire with the key in start position
3a) same with ground trigger wire ( 4 wire solenoid ) or body of solenoid ( 3 wire solenoid)
( I like to test V from the battery hot terminal to ground terminal rather than ohms as they give funny readings )

4) leave ground jumper in place ( from step 2 ) & try key start.
Starter turns = power connection good but ground connection suspect ( most common )
Confirm it by trying again, extra ground removed
I run a secondary ground from the grounding bolt to one of the starter mounting bolts & paint over both with liquid electrical tape.

5) Remove the trigger ( thin ) wire / wires from the solenoid.
Ground one & bridge from the hot terminal to the other.
Starter cranks = solenoid good.
Solenoid is not polarity sensitive, BUT THE WIRING IS so make sure you remove the thin control wires.
Note a thinner wire on the hot terminal is not a control wire. It is the main power feed to the mower.


From here on things become very mower dependant as starting circuits are getting changed all the time.
Basically the power goes in a loop from the hot side of the solenoid ( saves wire, no other reason ) through the fuse to the B terminal on the key switch then to the PTO switch then to the parking brake switch then to the solenoid trigger switch , easy peasy after you grow the 3rd arm. Use a test lamp and follow the power.
However a lot of mowers with a 4 pole solenoid, run a secondary ground control circuit to the ground solenoid wire through the lap bars.
Then to stop this interfearing with the normal safety function of the ground kill, it goes to a relay with the ground as the switched connection.
These are a PIA as the + control wire to the relay comes from the power loop above and the ground side of the control comes via the normal cut out functions of the lap bars.
Be very careful because if you have a system like this and accidentally send 12V down the ground loop you can fry the magnetos on some circuits.