Power Loss Merc 65 horse

NEED ADVICE:
I have an old mercury 65 horse engine on a 16' runabout. It runs great out of water, forward and reverse, revs smooth and everything. I took the boat out on the water and it won't rev hardly at all. the boat won't do over 8-10 mph. I have checked spark, fuel and compression... all of which are good. When its in the water it sounds like it "wants" to go, but is holding back... pulsing, but out of the water it screams. When it has a load on it, in the water, it won't go into reverse, it makes a grinding noise. I thought maybe it was over-propped, but the guy who i bought it from says it ran great with that prop. Can anyone give any advice? Could it possibly be a timing issue?
Thanks!!!

 

One thing that I forgot.... The engine is not charging the battery, I ran the engine a little over idle and hooked up my multi-meter, only batt voltage...Could this be connected to the power loss?
ANY HELP???

 

Youve got 3 problems, charging, gear cable adjusment( or stuffed gear) and possible carb and or timing advance to throttle.

All totally different.

 

Thanks JF, let me break down my problems as you said then, what can I do to remedy the gear cable issue? I am an auto mechanic, but have very little experience with outboards and 2-cycles in general. How do you check timing on this type of engine?

 

Like a throttle cable on a car when its off it should be off and giving no throttle but when you want full throttle the cable should be adjuted so that it gives full movement. You gearlinkage is the same, when you select reverse check that you have proper and full movement.

On a two stoke outboard there is massive advance. Take the cowling off and move the throttle lever then study the movement of the advance, you will see what I mean.

Theres many engines but normaly the manufactures have stages or marks on the throttle butterfly cam that should correspond with the correct advance.

The rate of advance is contolled by an adjustable rod from the throttle to the coil plate under the flywheel. Adjusting the length of the rod will alter the rate of advance. Shortening or lengthening this will advance the rate,-- not the max spark advance which is what youve set?

No charge ??? could be absalutely anything.

This is generall ---must get a book for specifications