Re: Pitch vs diameter?
You'll notice that as the pitch is increased the diameter automatically comes down, this is to help the prop by creating less drag in the water, with the theory that if you need that much more pitch your running a lighter boat, so don't need the extra power for pulling, usually at 19" pitch, and up it starts to become noticablely less power, but more speed. Chances are if your running at 4400rpm lightly loaded, and fully trimmed out with that aluminum prop, I don't recommend the 17" stainless prop, as it's harder to spin, even though it would be faster on 2 counts, 1) more pitch 2) no flex, and forget about the 19" pitch.
But, I could give you some tips to maybe get your RPM, & speed up! to make that 17" pitch work.
Here's what you do,
1) Adjust your carb idle mixture needles richer, with the engine off screw each one in gently till it stops, the make a note of the number of turns, then bring them both back out to where they were, and start the engine, let it warm up some, and begin screwing each one out counterclockwise, till the engine reaches the highest RPM evenly on both, that is the best richest setting, you might have to bring your Idle Speed screw down some if it's idling too fast. This should work, and your engine should love it! if not turn them in clockwise to the highest rpm's, or back to the original setting.
2) Next with the engine off, put the engine in forward, and open your throttle all the way at the helm, then take off your flame arrestor, and make sure your carb is open all the way, adjust the cable out to match if need be. Then don't forget to put it back, and in neutral when you're done.
3) Get yourself a good set of stainless spiral core (metal core) suppression spark plug wires, if you don't already have these. You should see, and feel an immediate increase in power. New spark plugs would help here also. (I prefer Champions)
3) Next, get yourself some syntheic blend, or full synthetic oil, 10-40W, brand is not important, whatevers on sale, and a new oil filter, and do an oil change.
4)you don't have to do this all at once, but when you have time, just the carb adjustments should make a big difference if not done before, this alone should take you to the top of your rpm range.
I had a 79'- 20' SeaRay bowrider with a 228hp 5.0 Mercruiser a few yrs ago it was a frsh water lake boat, never bottom painted, that regularly did 45mph, 48 trimmed out, and 50 one time, when I put a new aluminum 14X19 prop on it, in the Great South bay, Long Island (at sea level) I did all these things I mentioned to it, plus thru/hull exhausts.
Good luck, and let me know how it comes out, Mike
