Originally Posted by phil_edgecumbe
I have a 1:1 transmission and the standard 4 blade prop. I can't get the prop nut off to check it's dimensions.
You need to remove the prop to find out what you have before anything else happens. 4600 is definitely low and you should have no problem getting more than 5000 RPM from this but you'll need to run some tests, preferably real-time data collection.
FYI- they didn't just slap an engine in the boats and call it "Done". They did a lot of testing before the boats were released for sale, bot on-water and on dynamometer. While it was being tested, one of the measurements was in-cylinder temperatures and unless you have the ability to ensure that the changes you make will work without damaging the engine, work on getting it to run the way it did when it was new, first.