Bogging and stalling problems

[Raven Blayde]

I recently bought my first boat ( 70' 15ft fiberglass with a 66' Mercury 65hp on the back). First time I took the boat out, the engine would start right up, go into gear easily, would rev and run great, but the boat wouldn't move any faster then trolling speed at WOT. It was suggested that the rubber hub in the prop was bad. After doing some research, I found that the motor didn't even have the right prop on it to begin with. So, I bought a new Rubex prop (17' pitch) with the replaceable hub. Good news- The boat will fly with the new prop. Bad news- Boat stalls as soon as I put it into gear now. Every time I take it out, it takes about 10 minutes of fighting to finally get it to pull out. Once it finally does go into gear and run, it misses, boggs and runs horrible. After about 10 more minutes of running (at or around full throttle) the engine suddenly comes to life. The missing goes away, the rpm's go up, the boat levels up in the water and she takes off. At first, I was afraid the 17' prop was too big and causing this, but I'm begining to believe it's a problem the motor had before that just didn't show up since the old prop was spinning. The motor also uses about 3-4 gallons of fuel in a 20 minute ride up the river. Is that normal? Sounds like it's getting to much fuel to me, but I'm guessing here. Any help would be greatly appreciated.