525 Mercury Racing Engine pulling back once it hits 4200 rpm
 

When running up to 4200 rpm's the boat performs fine, once you hit 4200 rpm's the starboard motor pulls back to 3500 or so and back to 4200 like it is starving for fuel? No backfire? no cutting out of exhaust? Any ideas? No codes on the smartcraft it is a 2006 47 Fountain with trip 525's.