not getting max rpm, out of ideas

[turbocorrado]

boat is a 1997 wellcraft eclipse 2000s bowrider. 4.3 merc with alpha 1 gen 2. prop is 14.5x19 engine cover says max rpm should be 44-4800. manufacturer says top speed should be ~48mph. with trim down i am maxing out at ~3800rpm, i can trim up and get it to 4000rpm with a top speed of ~36mph. thought it was a tired motor last year, but it was rebuilt this spring and still get the exact same outcome. carb IS opening all the way, prop is new, motor is freshly rebuilt. i over trimmed it a couple times on accident while getting accustomed to it and the prop popped out of the water a bit and the engine revved to 4500rpms but thats the only time ive ever been able to get it into the max rpm range. im out of ideas, the only thing i can come up with anymore, which i really doubt is an issue is that maybe 14.5 diameter is to much for my boat

 

[Watermann]

More of a topic for the general forum.

The 14" sounds right and prop diameter shouldn't cause you to be 400-500 RPMs low, it's pitch that dictates the RPMs.. Was it the same prop as last year? Newer props have more cupping and aggressive rake than the older models and sometimes require a 1" to 2" drop in pitch depending on the prop. Is the prop stainless? What brand?

A heavy boat will do that, so a few questions about that subject... what is your load out? She's had 18 years to take on water in the foam flotation. Is the boat stored under cover all the time? Do you have a water leaking in that needs pumped out? Does water show back up in the bilge after you pull the plug and drain it? Does she jump up on a plane or slow in getting there?

You may just need to drop prop pitch to gain back some RPMs since lugging the motor is a bad idea.

 

[boater364]

Was the carb rebuilt with the engine? Also new fuel pump? Has the timing been checked? If your looking into the prop... I would also check your outdrive gear ratio is correct. Did it ever go over 4000 rpm? I also read all the time not to trust boat tach and speedo but sounds like you got something going on.

 

[Rick Stephens]

+1 on double checking the tach. They are notorious for being off.

You also want to check your speed with a GPS, if you haven't already.

 

[turbocorrado]

prop is aluminum and same size as the one i ran last year. i bought the boat neglected last year, i store it under a cover but from what i understand it was slipped in atlantic city nj for years with no cover on it, and it sank twice (guy decided to inform me of this after i had already paid for and signed all boat documents) currently has no leaks. i need to time how long it takes to get on plane.

rebuilt the carb last year, but it does have a spot where it hesitates at ~mid throttle if im slow top move the throttle. brand new tach last year. timing was set this year with the new motor.