I have a 2 year old Simplicity ZT 1644 with a 16 hp Kohler engine. I used the mower Sunday with no issues at all. Went back out to mow tonight (Wed.) and when I hit the key it fired right up but died almost immediately. I hit the key again and nothing! I lifted the cover and checked the cables at the battery which were tight when I heard a click from the solenoid. I realized that I has left the key in the run position. I closed the cover and heard the click again. Climbed on and turned key to the start position and again nothing. I left the key in the run position and just sat there. Now here is the weird part, about ever 25-40 seconds the solenoid clicks. I can't tell you this is normal or not because I am not in the habit of leaving the key in the run position without the engine running. If I hold the key securely in the start position at about the same 25-40 seconds it will engage the starter and even try to fire momently but dies right away. I checked and charged the battery, pulled the wires from the ignition switch and cleaned the connections with electric contact cleaner. Still no luck. I am fairly certain it is electrical, like something is overheating, maybe a relay? I am a auto repair shop owner but I have NO small engine experience at all. Any help would be appreciated.

I would not suggest holding the key in the start position for such a long time. Could be a relay. Sounds like this is going to be a tough one. Have you checked your valves? The fuel solenoid could possibly be making the noise. Have you checked to make certain all connections are tight and the cables themselves are not corroded within the insulation beyond just the terminal ends?