I have a John Deere LT160 with the Kohler CV460S 16.5hp engine. It was running fine and then while cutting the lawn it started to hiccup and backfire and then it lost some of it's power. It ran a short time at maybe half power before quitting altogether. Here is what I did:
1. Compression check- 85psi.
2. Fuel pump OK, pumping fuel.
3. Spark tests OK at my light tester. Spark at plug not blue, it was red/orange but seemed strong.
4. Sprayed starting fluid into carb when attempting to crank.
5. Engine oil about 1/2 quart or slightly more on the low side. Brought the level to the acceptable range.
6. Air filter was relatively dirty. Cleaned it .
Still will not start?
Took it to a small engine guy and he confirmed all of my tests. He was puzzled that it would not crank also.
He said that he would clean the carb but did not put much faith that that would solve the problem since he too tried the starting fluid. He did admit that he is not familiar with the "newer" engines since he is an older guy that is retired. He said that maybe there was something in the John Deere wiring /electrical that he might not know about but still felt that given the engine has fuel and fire it should start.

Any of you have any ideas as to what may be going on here?

Check your flywheel key .

Check to see if the valves are working right I had that problem and it did the same thing.