Your propeller is affected by wear. You will see decreased acceleration, poor hole shots, inability to carry a large load and your speed will decrease. Check your propeller by measuring the outside distance, diameter of the propeller. If you are running a 12 X 10 Big Blade, for example, the 12 is the diameter and the 10 is the pitch or angle of the blade. If you measure the propeller and it has 1/4″ or more decrease in diameter, then replace the blade.