The boat starts and idles great. I have noticed some missing a little or rpm drops at WOT but nothing severe. The prop that came on it was a aluminum 3 blade 15 pitch and the boat would top out around 40mph at 4400 rpm. I chipped a chunk out of one of the blades on the last time out so I swapped it for a stiletto 17 pitch advantage 2 3 blade that the previous owner left with the boat. Took it out today and top speed was 40mph around 4000 rpm but was having some missing down to around 3800-3900. Seems underpowered to me?
That all sounds perfectly correct to me, apart from the fact that even with the 15" prop the revs are a bit low.
Back to the change from 15" to 17". You increased pitch 2" and dropped 200rpm per inch. That is exactly what the book says each inch of pitch will change the engine speed by. You also didn't drop any top speed, again, that's right. But, at 4000revs, that's overloading the engine, seriously. Any minor faults (plugs, wires, cap etc.) will be far more noticeably.
Suggest you do a few things.
1. Do a full tune, including a compression check. New plugs, cap, rotor, and if the plug leads are still original, toss 'em and put a nice set of 8mm silicone leads in... If the engine's carbed and it's not been cleaned and had the settings done since new, get that done too.
2. Get rid of that 17" prop. It'll cause nothing but grief for your engine. Get the 15" repaired, or buy a new one. And put that back on. That is unless of course the above fixes whatever problems you have and the engine now makes enough power to turn the 17" at the 4400 to 4800 recommended.
Chris......
