A Universal M25XP is rated at 23 hp @ 3,200 rpm intermittent. Intermittent means the engine is only designed to handle full throttle/power for no more than 10 minutes before being throttled back to cruise rpm (enough time to dodge a big ship). The stock ZF gearbox has a 2:1 ratio. I've put a lot of props on those engines and my calculator says a Universal M25XP on a 34' sailboat (probably about 26' LWL) should have a 13" diameter X 8" pitch 3 blade RH prop, or a 14" diameter X 9" 2 blade RH prop. A 16" diameter prop is too big. The engine should rev to about 3,300 rpm at full throttle in neutral (high idle), and rev to 3,100 - 3,150 rpm at full throttle, top boat speed. The sealed injection pump/governor buffer screw you're adjusting probably changes the spring tension on the rack, and it could have been tampered with, so doing adjustments on it may change things. It would be good if you marked it so you can put it back where it was. If you want to learn more about it contact a fuel injection shop that does Denso fuel injection components and see if they can explain what the screw does (I keep meaning to do that myself). Hope that helps.