Originally Posted by Double Rigged (Post 3461784)

How many times have you run since spring? You have to take in account air temp, humidity, load etc. Most engine builders will tell you that you hp in summer months. My boat is a few mph faster in low humidity, low temp days. I would also check the amount of ethanol in the fuel.
Also regarding the engines keep track of your compression. As they age and it drops so does hp.