I have recently purchased an older boat with a 1968 mercury 65hp 650 thunderbolt with a mercontrol. I start the motor in neutral just like you would any motor, but the boat/prop move forward. If I move the mercontrol to forward, the prop/boat moves forward, but when moving it into reverse it moves it forward as well at almost the identical speed as in forward (which isn't the motors full speed potential that it should be, only aprox. 10mph). With the motor out of the water I've continuously tried to "play" with the lower unit shift lever and remount the lower unit to see if I could find neutral. No success! When turning the prop, it is not free. I make a hard click in the direction of forward. Same clicking noise happens when the lower unit is detached, with it not allowing me to move the prop in neutral unless forced. I took the impeller of and it appears in good condition. With the impeller off the prop allows me to spin it freely in both forward and reverse. I then slid the lower unit back on without the impeller, and it still stayed the same in forward with the clunking noise and not allowing me into reverse nor neutral. I wouldn't think it would have anything to do with the locking mechanism, but I could be wrong. I may have forgot some details, but I'm pretty sure that's everything I've tried thus far. Please give me advice! Anything is highly appreciated!