Slow Motion

I'm not familiar with that hull, but most play boats ( non racing ) of that size will be at their handling limit at the mid to high 40's, so you don't have far to go. First off, at one tank, the eng. isn't fully losened up yet, and the high speed needle may be able to be leaned down slightly for more RPM. Move your tuned pipe as far forward on the header as you can, without having the O rings leak. Those alum. wrap to forward and back headers are too long to tune the pipe properly. It could be that your center of gravity is too far forward, particularly with that large hard tank ( fuel ) ahead of the motor. Do you find the boat losens up and runs faster as the fuel gets low? If you set the boat on a flat surface, with a round rod ( broomstick, anything ) under the keel, the RTR boat ( half tank of fuel ) should balance at 26 - 28 % ( for your boat ) of the overall boat length, measured from the transom forward ( around 13" ). You will pick up some speed and not hurt the handling, by removing one rudder blade. A couple of close pics of your transom would be very helpful to see the set up on the running gear. Also, it's very hard to recommend a good prop without knowing the weight of the boat. While the Prathers do an OK job, there are far better blades to try. Try the above ideas and shoot us some transom pics, then we can explore some nice blades.