Mowed my lawn and put mower away (Cub Cadet 2166 w/ Kohler ch16 command single cyl). Mower ran perfect, no smoke. Few days later go to use mower and no start.Pulled plug and checked for spark. Good spark. Spray small amount of starting fluid into spark plug port and replaced plug. Turns over but no start or even try to start. MechANIC friend says he hears hissing...bad head gasket (I never heard hissing) so I change head gasket. Some black carbon on piston and head might be a little rich on fuel. Visually look at valves and push rods, look good to untrained eye. Tried to start ... no start. Put finger over plug port, seemed like low compression to me. I don't have a compression gauge. I can see visual signs of fuel going through carb. I have to think this is a compresson problem valves or rings. I am lost. Please help