I'm working on a John Deere Z trak F687 mower with a Kohler ch23s engine. The engine does turn over when trying to start but only starts sometimes, mainly after I put some gas in the carb a couple of times. When it does start, it dies soon after. I'd like to know what I should try next in fixing this mower. So far I have replaced the spark plugs, wires/coils, fuel filter (and checked the pump), air filter, cleaned the carburetor, and cleaned the cooling fins area. My next idea is to check to see if there is a vacuum leak of some sort, whats the easiest way to check this? I'm also working on a Kawasaki mule that won't run unless the cover is off of the air box so that the air filter is exposed. Thanks for any imput!