NS70A Issues

I have a pre 92 NS70A Nissan Outboard. It is on a 20ft pontoon and for some reason it will not open up under a load. I can get it to open up in neutral or in gear without a load but once I put it in the water it sounds like it is bogging down. Compression is 150 psi top and bottom both plugs are firing and I removed both carbs tore them down completely and dipped them both so they are spotless. The Woodruff Key sheered on the fly wheel and I replaced that. How do I link and synch that model engine? I can not find anything online on this model. The repair guy I use just wants to start changing parts until he finds the issue. That can be pricey. Could some one possibly help me Out?

The 70A is pre-1986. The A2 might be as "new" as 1992, but you have a really obsolete unit. No carb kits, no water pump kits (but the bare impeller is available).
Was this rig working OK at one time (if so, what changed?), or was it recently rigged (or did it Never work right)? Most of the time these sort of rigs just have a too-steep prop pitch. What pitch are you running? What is the WOT RPM in calm water? What do the plugs look like?
You can probably infer appropriate link and sync from the Factory service manual for the Tohatsu 3- and 4-cylinder models, available from any dealer, but the original manuals are long gone... Elvin at Solution One in Tampa might have something, but I can't guarantee that.

Its a 2 cylinder and its never worked right since I have had it.

Tohatsu has organized the obsolete manuals into two separate "combined" manuals; the 1 and 2 cylinder manual (that goes up to 40 hp), and the 3 and 4 cylinder manual.

No one I know has a service manual for the 70A any more. You could call Solution One Maritime in Tampa, and ask Elvin if he has a manual, but I don't know at this point.

If the motor has always been sluggish, it may just be a wrong prop pitch. Toss a good tach on it and check the WOT RPM. There are still some props available for the 70A/B models.