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JD L100 with 17.5 B&S

Used weekly, works great... at one point I thought the solenoid went out as I had to start shorting it to start... did that for a while with no problems. Finally ordered a replacement...

Replaced solenoid and battery... wont start with the key, but still starts and runs fine jumping the solenoid.

Today... jumped solenoid and was getting ready to mow... but at idle it started to lightly surge and then die. Got it to start again, put it full throttle and it started to surge again, engaged PTO and it died.

So, surging idle and dies under load.

Now.. wont start at all.

When I short solenoid it still turns the motor but it will not start.


What I know:

Have spark
Have fuel (though maybe not enough? when I dc the fuel line at carb, while cranking fuel trickles out.)
brake switch is good
PTO switch is good.

NO voltage to purple wire at solenoid

Thoughts?

also add that I disconnected the ign switch and cleaned all terminals.... nothing

I opened the switch to inspect and there was some wear... cleaned up contacts and reassembled, still no start with key or shorting solenoid.

Could a defective switch cause this?

Very first thing I would check is the battery and if you get it started the charging system. If you know your battery is in great shape I’ll post a testing procedure.

Does the carb. have a solenoid on the bottom of the fuel bowl? If so I'd check that out for operation.

Battery only has a couple of hours on it.


There does appear to be a solenoid on the carb... How do I test it?

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.
+ on the starter first then - to a good ground near the starter ( drain plug of lift hook are good )
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

5) Remove the trigger ( thin ) wire / wires from the solenoid.
Ground one on a 4 wire solenoid & 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.nd from the grounding bolt to one of the starter mounting bolts & paint over both with liquid electrical tape.

Battery and starter are good.


on a 4 terminal solenoid, which is the trigger wire?

tom3 said:

Does the carb. have a solenoid on the bottom of the fuel bowl? If so I'd check that out for operation.

Click to expand...

It does. I removed the solenoid and the shaft moves freely.
Not sure how the circuit on that works.

Either way, I should still be able to turn the key and have the motor turn, regardless of if it starts.

Still with that shaft in the up or down position the motor only starts for a moment and shuts off within a second or two

shibbershabber said:

It does. I removed the solenoid and the shaft moves freely.
Not sure how the circuit on that works.

Either way, I should still be able to turn the key and have the motor turn, regardless of if it starts.

Still with that shaft in the up or down position the motor only starts for a moment and shuts off within a second or two

Click to expand...

When you turn the key on and off you should be able to hear it click under the carb.

ILENGINE said:

When you turn the key on and off you should be able to hear it click under the carb.

Click to expand...

I hear nothing.

Should I assume that its fried then?

Is there a way to correctly bypass it to confirm it was my problem?

The next step would be to make sure that you have 12 volts to the solenoid. Red to grey wire, and black to black wire from your meter. if no voltage then move the black lead to a known good ground. If no voltage in those test then time to start backtracking the wires. the 6 pin connector between the engine and the mower wiring harness is a possible place for problems.

If you have voltage then remove the solenoid and make sure the plunger can be moved by hand freely. If it moves freely and you have 12 volts then you can assume the solenoid is bad. You can substitute a carb bowl screw from another carb that didn't have solenoid, or if in your case the plunger doesn't work with battery voltage applied then you can clip the end of the plunger off and then test to see if it will start. worse case scenario is a loud after fire from the muffler when you shut if off.

Sometimes you can’t hear it but if you put your hand on it, you should be able to feel it. Another way it to take a long screwdriver, put the tip on the solenoid and the hand on your ear. Poor mans stethoscope.