1985 Evinrude 40 hp. Reverse problem

The motor had not run in 5 years. I went through most of the engine and replaced spark plugs, water impeller and cleaned everything up. I the motor runs great now except I am having one problem. When I put the outboard in forward the prop engages and pushes the boat along.

But when I put the outboard in reverse the engine engages but does not have enough power to move the the boat in reverse.

I am not sure why I am having this problem. Any ideas?

Sounds like you need to adjust your throttle and shift cable. The cable is engaging the shifter, but not allowing you to rev the motor up.

On generic control boxes (Teleflex) there are multiple places to attach the cable ends. I have run across this a few times in the past and if memory serves me correct one of your cables is in the wrong location inside the box. If it ran correctly at one time then obviously disregard this.
However......at your engine.
The control box must always be adjusted to match the engine, the engine shift lever should never be moved or rotated in the least to hook up to the control cable. Always make your adjustments on the cable and never the engine.
Find your "slop center" on the engine shifter (in neutral) and your "slop center" on the cable end and adjust your cable to just slip over the stud in neutral.
Same with throttle. Move your linkage to the idle stop and match the cable to it. Adjust it only tight enough to gently bring it back to its stop every time. Not tight against it.

Had the chance to look at the motor and run it today. Again forward works perfectly fine no problems there. When I put the motor in reverse the prop spins in reverse but not fast and it does not pick up speed when increasing the throttle. Also I notice today a vibration when applying a little more force in the shifter handle. Not sure what this means. Any help would be great