B won't start

Cut of tractor 2 days ago and went back today and would not start. First thought was a dead battery, but jumped it and only a partial starter movement. next jumped directly to starter post and still would not turn engine.  Had not set in rain or moisture.  Gas had been cut off.  Oil level normal. Pulled tractor and engine turns but did not hit a lick.  Points are not stuck and opened and closed when pulled.  Ran and started good when left and no hint of a problem.  Starter spins on bench. What might be the problem and what would discharge it when setting.  Switch was left in off position. Please help with any suggestions at this point.  Thanks 

There is some missing information here. What is different about it not starting this  time from last time? Is it that it will not turn over like it did before, or it will not turn over at all? Explore that as a symptom, then do diagnostics from there. It sounds like it will not turn over, and it did so before. If that is the case, then the problem is more than likely in electrical flow through the starter, and all connections, including ground, have to be checked and verified. While you are at it, check and see that spark is available at the plugs. Pull one out and turn the engine over with the switch on to see if spark is available. Good luck.      

Sounds like you have more than one problem afoot, and it isn't likely that more than one unrelated failure would occur at the same time.  Since it seemed fine prior to some incident, either a failure has caused another failure, or the incident had an effect on more than one aspect of the machine.

Here's some notes for you:

- First things first- if it isn't cranking, you'll need to find out, and resolve that issue.  you KNOW that the battery is dead, so lift the battery caps and observe electrolyte level.  If they're all uniformly low, add distilled water and charge it up... and make note to check charging system once she's running again.

 - Just because a starter spins on the bench, doesn't mean it'll crank an engine.  It DOES indicate that it's not internally bound-up, but if you still have it out, it'd be a good idea to pop the covers off and make sure the brushes are all moving okay, and that you don't have a blasted-out end bearing on the brush-side.

Ground strap and positive strap, starter switch are all important to check, too.  If you bend a battery cable, and it feels 'crunchy', moisture has wicked in and corroded the copper- replace it.

 - Just because the contact points are moving, doesn't mean they're closing all the way, and just because they appear to be closing, doesn't mean they're making sufficient contact.  Oftentimes, I've had points become contaminated, and as a result, will close without conduction.  Check for spark at the plugs... and when you do, make sure the spark is nasty-mean, not just a little spark.

Once youv'e got that, if it still doesn't start, post what you found, and we'll take it from there.

Went back this afternoon and remounted starter, cleaned cables and redressed battery connections. Positive battery connection looked good, but post was corroded, so I redressed it.  Then it started promptly.  Had apparently lost voltage to distributor as well as to selanoid to starter.  Now all is well. Thanks for all help. George