As a first step, you might just pull the dipstick and see if the oil feels/smells like gasoline.

Remove the spark plugs, ground the wires to prevent spark and then try cranking.
Hopefully the carb needle & seat is leaking and you filled the cylinder(s) with gas, hydrolocking it.
That sounds like the lowest cost scenario. Otherwise, it sounds like something broke internally.

If it's not that, remove the valve covers an look for something obviously amiss. You have 2 cylinders, so you can compare one to the other.

Have you checked and cleaned wiring connections from battery to starter and the battery to ground.
Usually a Auto parts supply will check battery and starter for free, you need to remove them.

Thanks for the suggestions. I checked the dipstick and no gasoline smell. I took out the spark plugs and tried cranking it. No change. Like I said, when I turn the key, the starter engages, the flywheel turns an inch or two if at all and then everything stops and it makes kind of a humming sound. The flywheel turns manually. I took the valve covers off and looked at the valves. All 4 look the same. Nothing noticeably different. I thought maybe the valves needed adjusting, but wouldn't it crank better with the spark plugs out if compression was the problem? I could try adjusting the valves, (I've never done it, but I've read about it), but I don't want to mess with them if the problem sounds like something else.
So any other suggestions or should I load it up and take it to a repair shop?

Removing the spark plug eliminates ANY hydro locking or compression problems, so we have that eliminated.

IF the flywheel turns freely by hand, my guess is the starter motor is "toast.
However, there are a couple more tests we can do if you have a voltmeter.
IF you don't have a voltmeter, about all you can do is insure all the connections are good.
Battery posts to cable connections. The OTHER ends of the battery cables, Starter ground to engine and engine ground to tractor frame.

You could remove the starter motor and try jumping it with booster cables, bypassing the solenoid completely, as a final check. It should spin!

Yeah - put the starter on the ground and bypass the wiring with a set of jumper cables to see what happens.

Also - once you get around to getting this resolved ... do spend a bit of time getting your valves adjusted - its not hard - and your motor will start much more easily...

but as mentioned earlier - as said with the plugs are out you dont have any compression problem.

im thinking bad ground, solenoid or ignition switch.

good luck

Thus engine has hydraulic lifters.
Valve adjustment isn't an issue!

try starting with the basics of any motor. Pull out the spark plugs and put your finger in the spark plug holes. Manually crank the flywheel a number of times. Make sure you feel the compression. That eliminates any broken parts. If the piston goes up and down and the valves are working, you will feel the compression. That tells you you didn't shear a key on the flywheel, it tells you the valves aren't bent or broken. It tells you you didn't put a hole in the piston. It tells you the piston rings are still good. It's a good starting point.

I took the old starter and the new starter to an auto parts shop and they both tested fine. I guess it's time to give up and take it to a professional. I found a shop that charges $55 an hour, which I guess is about the going rate in my area.
At least I tried, and I learned a lot in the process. Thanks for all of your input!

When you say "The flywheel turns manually", you are turning it through complete revolutions, aren't you?

IF the engine is free to turn AND the starter is good, it leaves these as possibilities-
Bad solenoid. battery or connections.

Think Timing...
For power to be developed, the ignition of the compressed air/fuel mixture must take place at exactly the correct instant - just before the piston reaches Top Dead Center (TDC) on the compression stroke.
Timing is set on older mowers with point type ignition systems by adjusting the point gap and generally only changes due to wear. However, these changes are gradual and unless the points come loose for some reason, will not likely suddenly prevent the mower from starting. On newer electronic ignition systems, there is basically no adjustment as the position of the electronic ignition coil/module fully determines ignition timing and this is fixed.

However, timing can be grossly messed up if the flywheel key gets sheared and the flywheel then rotates a fraction of a turn on its mount on the crankshaft. The result may be a mower that does not start, backfires or runs erratically, lacks power, won't run and/or start when hot, etc.

This is very likely to happen should the blade strike a rigid object causing the mower to stop instantly. In this case one or both of the blade lock key and flywheel key have sheared to (hopefully) protect the very expensive internal parts from damage.
There are likely not going to be any timing marks for that old timing light you have sitting gathering dust somewhere. The only test really is to inspect the flywheel keyway to determine if damage has occurred.

Timing would have NOTHING to do with the engines failure to rotate when the spark plugs are out!

Bill...he did say the engine rotated...he said it moved an inch or two.
That sounds like a sheared key.
I think DeereJohnny may be on to something.

I can manually turn the flywheel a complete revolution. Sometimes it's more difficult to turn, but I can always turn it.
When I try to start the engine it does rotate slightly and then abruptly stops. It doesn't matter if I'm turning the key or jumping the starter with my truck battery. It also doesn't matter if the spark plugs are in or out. It always does the exact same thing.
I know I'm missing something, but I've got to get this fixed. I dropped it off at a repair shop this morning and the mechanic didn't have time to look at it, but he did turn the key once and said "sounds like the starter is bad". I told him the starter tested good, so he's going to take a look at it in the next few days. I'll keep you posted on the outcome, in case someone else has a similar problem. Thanks everyone.

My lt1000 spins then stops too. What was your result?

Try jumping across the solenoid with a screwdriver,make sure the key is on. If it starts one of two things.
1: safety switch is open
2: solenoid is toast.

"This is very likely to happen should the blade strike a rigid object causing the mower to stop instantly. In this case one or both of the blade lock key and flywheel key have sheared to (hopefully) protect the very expensive internal parts from damage."

Well I am coming late to this but hitting something with a blade of the mower deck of a riding mower with belt drive and shearing the key of a 20 hp Kohler is a little unbelievable especially since a Kohler uses a steel key, not a soft key like B&S and I never heard of a properly torqued B&S flywheel shearing a key of a belt driven deck either for that matter.

Walt Conner

craftsman 20 hp is it possible my starter is shorting out and causing battery to die? starter still works

robert72008, you should begin a new thread on this machine's problem.
It is highly unlikely that your stater is shorting and killing your battery. When you start your new thread please give the proper engine model number (from the engine) and also tell why you describe the battery as "dead". How old is this battery? Is your complaint that the starter engages but will not "spin" the engine? If so you may have valve adjustment issues, but a better description could clear up some uncertainties.