Saving Old Seagulls

And I allways thought that the 1/4" hole in the SD water pump housing was put there by Seagull to make them run a little hotter than they would without it.

Didn't they run a less efficient water pump post war, to save them the cost of drilling this hole & doesn't the water jacket cover the entire cylinder head, unlike the detachable air cooled head on the Centurys & 40's powerheads.

Wasn't this the era before the advent of 2-stroke oil so that they had to run on 30 grade motor oil, with all the problems of oiled & wiskered plugs if they ran too cold

I was pointing out the fact that the amount of water expelled cannot compare to a century simply because the hole is so much smaller
looks to me to be only half the size

Sorry I misread your post I thought you were advising 102 owners to redesign the cooling system.

The internal diameter of the copper feed pipe from the impellor up to the block is the same in all the different models. That's the smallest diameter, that's the greatest restriction on water flow. Unless the block is clogged, of course.

The little block on the exhaust has a very small outlet
smaller than the internal pipe
it also goes through to the inside of exhaust but does any water go in that way
as said against exhaust pressure ?

Yes it does. That's the whole point of that cooling system, spent coolant cools the exhaust, the idea being that cooler exhaust gases are reduced in volume, thereby quietening the motor.