I have a 48" Bobcat with a 15.5hp Briggs. It worked flawless for 4 years and now won't start up on the second pull like it has always done. I have to choke it and pull the cord, then release the choke and pull about 10 more times before it starts up. Gas actually drips out of the muffler when it starts.
I tried new air and gas filter, new spark plug with no change at all.
Any suggestions?

Check for spark, otherwise take off, disassemble and clean the carb.

Common cause is fuel left in tank without a fuel stabilizer.