Will Crank, But Will Not Start... 417A with a 17 HP Kohler Engine

[the jeep driver 29]

Hello.   My 1985 Wheel Horse 417A with a 17 HP Kohler Engine will turn over, but will not start.  It looks to be getting fuel, I can see gas in the carb...   I did try starting fluid, no start.  I changed the spark plugs, as the old ones were due anyway, and used an inline spark tester to verify spark.  I don't know what to test next.  Any help is appreciated!  

[ri702bill 12,762]

Fuel, air, spark, & compression. Ya need all four to rave it run.  The spark - is it a strong blue-white color or plae yellow? Is the timing correct ? - right spark at the wrong time in the cycle equals a no run condition.

[953 nut 68,365]

This manual should be helpful.