Thing is, you aren't around to Reap the Payout.
YEARS ago, MAD Magazine had a Drawing, showing a Corpse with Big Smile, cause he had a big Life Insurance Policy...
In the Paragraphs above, are some clues as to where the Problem might be
You are assuming the Pump is fine, cause you rebuilt it.
There was no change in how the engine ran when 2 of the Plugs were disabled.
How did you determine the Carbs were clean Internally?
Where did you verify the Fuel...
"Chugging and Clunking" Noises, describe a large variety of Issues, from Misfires through Impacts. Best to pull the Boat, just to make the Inspection much easier
The 100:1 Ratio was retracted by OMC, probably because of lack proper Mixing, but they claimed it was because of a lack of Oil on the Internals potentially during extended Downtime, was the Reason. The early VRO System did go leaner than 100:1 at Idle, but even it, was providing about 50:1 at WOT.
No, it is not the Size, Airflow wise, that the Engine was designed for. Incorrect Carb size, and resulting improper operation, make an Engine a Chore to Operate, if it even runs. But some people have to Experience the Problems/Issues themselves....
Yes the Models with Power Trim from the Factory did have a 10 Amp Alt. I would verify that the Dash Voltmeter is Accurate, and same goes for the Tachometer, as you would need to have a very Light and Small Boat to get that engine over 5500 with a 19 in prop, unless you have a lot of Slippage...
Pretty much every Used Engine I have ever seen as been described as running Perfect the Last Time it ran, even the Ones that had Broken Piston Rings, and even a Hole in the Crankcase...
First things first.
Is there Oil in the Gearcase?
I would suggest an Inspection of the Water Pump, and a New...
That Engine's charging System is Unregulated, and as Rpms increase so will the Voltage. The Battery is the Regulator, and while the Voltage is a but high, the Current is not that great(If I recall, the Charging System was rated at 6 Amps).
However, what exactly is the the Rpm you get when it is...
The 33.3 cubic in twin was introduced in 1970 as the Mercury 400, by 1972, it was renamed the 402. In 1979 it was renamed the Mercury 40, and in 1984 was changed to a 35hp, likely due to 'Prop Rating'. It was made for a few more years. It did share gearcase housing size with the 44 and the 49.6...
Water coming out of the Exhaust Vents is Normal, Exhaust coming out of the Telltale once the water is coming out of it, is Not Normal.
It should have water coming out of the Telltale within 30 seconds. How Old is the Water Pump Impeller? Better yet. How long have you owned this Motor?
It took only a few seconds to Download the Video.(I have a slow, 30mb copper DSL service. Phone company has been threatening disconnection if I don't switch over to Fiber).
Watching the Shift Lever boogieing like it is listening to 'shaking all over', you might consider pulling the Gearcase...
If you have a Dremel you could try cutting several Slots in the Crank Shaft, then use a Chisel on them, along with a bit more Heat. Just don't cut into the Drive Shaft. You could also try Chilling the Drive Shaft with some CO2, whilst Heating the Crank Shaft. Removing the lower Crank Shaft...
