I've had the water pump apart about a hundred times now it seems. No obstructions in the pump. It pumps good water to the tell-tale. Beyond that who knows but as you can see the passages are clear, the holes to the front and back of the jacket are open.
It has 3 individual carbs. Oil is injected post carb into the reed plate i believe and is "metered" into the cylinder according to rpm by virtue of the gear driven oil pump that increases flow with rpm. I have a low rpm problem only with the alarm.
I am thinking oil system now. Can't be anything else. Water flow is a good a i can make it with all new parts.
Regarding the scoring in top cylinder. You can see it but you can't feel anything. It isn't deep enough to actually feel even if you drag a finger nail across it.
Re motor height, no jack plate only tilt trim. Cav plate is even with our just a hair above bottom of boat. I haven't messed with it since I've owned it. I've owned it about 7 years. Problem first started in around March of 2020. I do tend to have more issues when idling trimmed up though but i typically trim up some when i idle so it may be coincidental.