PS.  I see you are on Lake of the Ozarks MM  I am at MM 13 on the Niaguia Arm  Been there over 20 years

I have a 5.7L carb merc crusier that doesn't fire over within a few seconds after 10 hours or so of use.  I had the carb re-built by the dealer about  July 2003. Recently within 30 hours of  use the plugs are fouled and you need to crank it for about 30 seconds to get it to start.  Compression is good on all ...