I have a 24hp Briggs ELS on a Scag Tiger Cub with about 50 hours on it. 2 weeks ago I started having a hard time starting it, but only on the first crank of the day. It was like the battery was dead or a safety was disengaged. All I got was a "click" when I turned the key and finally after a minute or two it would start. I've never had a problem after the first crank. I took it to the dealer and of course it started perfectly. They changed the plugs and the fuel filter and I have had no problems until this morning when the same thing happened again. Any thoughts on what could be causing this?