Small Engines (Lawn Mowers, etc.): riding lawnmower, castrol gtx, cylinder gasoline

Question
David, i have a john deere x300 riding lawnmower.it has a 17hp Kawasaki 2-cylinder gasoline powered motor, with 35hrs total operating time.i am currently using castrol gtx 5w30, but would like to change to mobil 1 5w30 synthetic.what would you recommend , continue using the castrol or switch to mobil 1.thanks john

Answer
Now that you given the engine time to break in, I would put Mobil 1 in the engine.  Remember, just because its synthetic doesn't mean you never have to change it.  Still change it according to Kawasaki recommendations.  

I have personally been involved in testing with air cooled engines and Mobil 1, and I give it "TWO THUMBS UP"