Hi, I just recently bought a 1989 astro quickfire bass boat. It has a Mercury XR4 150Hp outboard motor on it. Today I just tried to start it and it did. But it revved really high and I turned it off right away. Now the flywheel wont turn. When in neutral the prop spins. Then in forward the prop spins but makes a really loud clunking noise in the lower end about half way down. I put it in reverse the prop does not spin either way. Any idea on how bad the motor is now? Could it be fixed easily if I got a service manual?