Craftsman Riding Mower Won't Start?

I just got this Craftsman riding mower with 18hp twin Kohler magnum from a friend. He said that 2 years ago he had ACE do a valve job. Then he picked it up and drove it on his trailer. When he got home it would not start. If my Craftsman riding lawn mower just got $600 valve job wouldn't the engine be all clean? So here I am with it. It turns over nice and strong, but won't start. I did drain all old fuel and took carb and fuel pump off, it was all dry. I cleaned it all and fuel is coming through now, but it still won't start?