If you are using the original fuel tank there might be crud plugging the filter. undo the screws that hold the assembly to the tank and check to see if it's clear. Any Merc was designed to run full throttle for hours.
I have used the steel insert and it went well but you have to use Loctite to hold it in. It seemed to be better than a Helicoil as it gives a complete steel plug hole.
I think it's thick splined washer, prop, castle front thrust washer, then nut, there should be no play in the prop, unfortunately the seals in the casing have been damaged so exhaust could leak out around the prop - PO was a real loser!
It's a limit switch that you can set to stop the trimming before the motor over revs
you set the small bracket on the side to stop it when you've found the right trim setting. Test it in the water on plane.
It won't run right until you set it up in water, the back pressure and prop resistance change the way it performs. Muffs are good for winterizing and pre-season starting.
You set the low speed needles (with the motor warmed up), in forward, running in the water at about 900 rpms. Set them 1 1/4 turrns out to start the process. Revving the h**l out of the motor in N with muffs can lead to destruction.
Clamp the driveshaft in a vise horizontally then use a box end wrench to undo the pinion bolt, use a rag on the wrench to keep it from damaging the internal threading.
More details:
I had a 1975 LU and the bearing carrier was stuck so bad that removing it ruined the housing, if you soak it with the propshaft vertical in penetrating oil for a while it might free up (I just bought a new LU)
Another alternative is buying a complete motor for parts with a good LU.
I posted this for shift setup: This is how I do it in about 60 sec.: Turn the LU shift shaft by hand counter-clockwise until it
stops, then with Vise Grips tight on the bottom of the shaft turn it a
few more degrees CCW until it clicks into a stop, this
should be neutral - check by turning...
