Kohler 15.5 OHV - runs rough / smoke and gas out exhaust at start

I have a Kohhler 15.5 on a Craftsman rider. It runs / cuts but runs rough and spits gas and black smoke when I start it. It always starts but doesn't start as easily as it use to. I bought this rider used for $350 4 years ago and have only novice small engine repair skills so I am wondering if it's worth getting it looked at or should I just start shopping?

Thanks,
Jim