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I have a John Deere 18.5 hp Briggs & Stratton riding mower that will not start. The battery tests 12.46 volts. All filters are new. Fresh gas and wire and cable connections correct. A new start switch two years ago. It will not turn over enough to start and will sometimes hum as if the solenoid is stuck or broke. One time it backfired when trying to start. I do not know how to test beyond what I have stated here. Does anyone have a suggestion from what to do at this point? Thanks!!
Don B.

How old is the battery?

Mikel1 said:

How old is the battery?

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Installed new in April 2013. States it has cold cranking amps at 275. I have cleaned the terminals and connections and that should not be a problem. Thank you!!

Don B.

Three years old I would have it load tested to rule it out. This can be done for free at most auto stores that sell batteries.

i agree.

Firstly do not rule anything out.
First tesst remove the spark plug and try again.
If engine turns over all eletrical systemas are A OK.
The spark plug needs to be earthed but well away from the pulg hole just in case the cylinder is full of fuel.

Mikel1 said:

Three years old I would have it load tested to rule it out. This can be done for free at most auto stores that sell batteries.

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After the first reply from Mike, I hooked up another 12 v tractor with jumper cable and tried it. It would turn about 1/2 revolution only. Will have it load tested and the plug checked. Thanks to all who replied. I am going step by step to locate the problem. I appreciate all who responded. Thanks!! Don B.

maybe you'll figure it out quick! i know you're anxious to start cutting grass lol

donkb said:

After the first reply from Mike, I hooked up another 12 v tractor with jumper cable and tried it. It would turn about 1/2 revolution only. Will have it load tested and the plug checked. Thanks to all who replied. I am going step by step to locate the problem. I appreciate all who responded. Thanks!! Don B.

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These things are important.
Now do as I asked and try it without the spark plugs.
If it turns over OK the pull the rocker covers off , check the operation of the valves , they should all sit at the same height and go in the same distance.
Vsual is good enouhg.
If they look OK then adjust the valve lash.

Mikel1 said:

Three years old I would have it load tested to rule it out. This can be done for free at most auto stores that sell batteries.

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Took your advice and sure enough battery failed load test. So, I replaced the battery and plug as well as cleaning battery contacts real good. I got it started but then this happened. The switch in the start mode would turn the engine for a fraction of a second and disengage. I tried it for three or four times and it started. When the engine is warm, it starts immediately. I know that sounds strange. Last cutting season, I noticed it doing the same thing on occasion. Any thoughts on that?? Thanks, Don B.

faulty safety switch? faulty ignition switch?

bertsmobile1 said:

These things are important.
Now do as I asked and try it without the spark plugs.
If it turns over OK the pull the rocker covers off , check the operation of the valves , they should all sit at the same height and go in the same distance.
Vsual is good enouhg.
If they look OK then adjust the valve lash.

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Thanks for the information. I was one step from the procedure you suggested. Decided to recheck the switch. Would not make contact/turn engine over in the start sequence every time. After I got it to start and it warmed, it would continue to start easily on the subsequent start attempts. Believe the problem is the switch and I will replace. Don B.

good deal!