Small Engines (Lawn Mowers, etc.): Engine Timing for John Deere GX75

Question
I just purchased a John Deere GX 75 with a Kawasaki 9 hp (Model FC29OU-CS10, I think).  It started/ran fine at the dealers, but after transporting it 350 miles on the back of my small utility trailer, it will not start.  Has lots of spark, is getting gas, but wants to backfire through the carb - Timing ?  What should I do and how do I check the engine timing?

Answer
Ronald

Have you checked the float inside the carburetor? it may be stuck open causing too much gas getting to the spark plugs,timing would not be affected if you just transported the mower.
What may have happened during the trip the float got bounced around and came loose.