I have a kohler marine gen set I started it today ran for 20 sec. then shuts off. Had it serv. Last year. Changed wire harness and choke. Getting gas spark?kolher 5e
New Rochelle ny 10805 please advise

Did you check to see if it needs oil

If it just runs for 20 seconds, does it restart? Could be dirt in needle valve if carbureted, stuck fuel float, restricted fuel line.

You had it serviced last year, and should have serviced it again this year before you tried to start it up, or changing parts. Especially if it's been idle for an extended period.

Kohler Engines (http://www.kohlerengines.com/maintenance/maintenanceSchedules.htm)

Did you leave gas in the tank over the winter?