Take a look at the Yamaha break in procedure. Then take a look at the Mercury Marine break in procedure.
Then you might have some idea as to why Yamaha's suffer from making oil at a higher rate than do Mercury's.
Yamaha calls it Primestart. An automatic fuel enrichment system. Adds extra gasoline when the motor is cold.
Not uncommon for a 21 year old motor to be seriously in need of a thorough cleaning.
It is a stretch, but what with some carburetors having miniscule orifices and passageways perhaps the slightly higher viscosity gas/oil mix might be hindering the flow of fuel to the motor.
If 75/1 works better than 50/1 one could presume that the Yamaha recommended 100/1 gas/oil ratio might be better. Cost little to nothing to give it a go.
There are a number of Yams designed to run on 100/1 premix and have no less of a life than those designed to run on 50/1, or on auto-lube which in some cases has a ratio of 200/1.
Where in the world are you? I have no idea what RNLI means.
When you say "I had the neutral switch bypassed on the Evinrude" I am presuming that you mean the control box neutral safety switch was bypassed. Not a particularly smart idea but so be it. To each his own.
There is no wire to bypass in a Yamaha motor. If battery power is provided to the motor...
I remember the days of 16/1. Folks were scared to go to 25/1 and added extra oil.
Then they went from 25/1 to 50/1. Folks were scared to go to 50/1 and added extra oil.
Now they go to 100/1 and folks are scared to go to 100/1. Adding extra oil.
It is not abnormal for there to be a period of time before water starts coming out of the tell tale. A minute's time would not concern me.
Having said that, when was the last time the water pump was replaced?
Is the rectifier installed on the motor in addition to this mysterious part?
My guess is that it might be an upgraded rectifier or perhaps a rectifier/regulator. But...
