I'm running a 21' 2003 North River Commander. It has a 330 HP, 5.7 L 350 with just over 300 hours and a Hamilton 212 jet. We bought it in the spring and ran it on the Yukon/Nowitna this fall. We were really pleased with how it performed with two exceptions. First, it tends to porpoise before you get to WOT, particularly under load. We installed trim tabs over the summer, so that's not the end of the world.
More concerning was the fuel consumption. We were hunting moose and running pretty heavy (both ways, fortunately ). WOT is about 4100-4200 RPM. We ran at about 3800 RPM. Ended up running about 29 MPH on average and burning about 14.5 GPH. We were hoping to get between 3 & 5 MPG, but only ended up getting 2 GPH. That was disappointing.
Questions for those of you with more experience than I have: Am I correct that should have been getting a bit better mileage? Any idea how much better? We had two guys, TONS of food and gear, an extra 115 gallons of gas, Zodiac, generator, etc.). Somebody suggested that we probably need to have our impeller rebuilt considering the hours on it, RPMs, and fuel consumption. How do I know if that's legit? Other ideas about why our fuel economy might not be great or what we can do to improve it?