Only 4 knots?
Hmmm... My first boat was a 24' Challenger Clipper. Roughly comparable to your 25 footer. I had a 9 horse mercury powering it and it would drive the boat at it's hull speed which was about 6 knots. Your 7.5 should move your boat faster than 4 knots unless you were pounding into some weather. I'm not sure what you should look at; but that is at the low end for speed, under power; especially with an outboard. You might want to check your prop for the correct type and get the engine tuned. Also, is there a lot of marine growth on the hull? If so you may want to haul out for a good cleaning and paint job. Bon Chance!
