I have an OMC, 4 stroke 9.9, outboard, which runs beautifully with one exception. When I put it in reverse gear and apply throttle, the engine pops up and the prop comes out of the water. I have looked at the lock down mechanism, and can see nothing that appears unusual, the engine locks OK in the up or down position. It will not budge when in the down position if you try to lift it, but put it in reverse and it comes right up. What's the problem here? Thanks, SJ