reverse trouble?

[DutchMerc]

I have a Mercury 402 longtail outboard, and i ran into a problem last weekend. I took the motor out for the first time, and it seemed to have some trouble running on idle. Everytime i put the motor in neutral, it just stopped. I tried to set the idle-srew on the carb, but it gave me some trouble. To get back to the dock, i needed to open the throttle just a little, (i have a two-handle Mercontrol) and than throw it in gear. Forward went OK. But i noticed that when i did the same thing in reverse, the motor tilted and the prop got airborn.. The strange thing is that this did not happen every time. Most of the time i could go reverse even with WOT, but every now and then the motor did not lock. The problem might be in the lower-unit, as the impellor has been replaced recently. When changing the impellor i noticed the cam on the shift-shaft (behind the waterpump) was worn, and I replaced it. Is there a procedure to align the cam on the shift-shaft? I assume this cam should lock the motor when in reverse....