454 magnum"bravo1" 9 mph tops on 26 foot

[russell veldman]

Help... I have a 1988 Celebrity 265 with 454 magnum, carburetor, bravo1 ... engine won't go over 4000 rpm and boat will not plane. Engine/drive run smooth and seems strong. 285 hrs on engine (original).
Changed plugs, cap, wires.... The boat came with a SS 16x15 prop that the previous owner changed to a new aluminum 16x14. At 2000 rpm, runs 8 mph. At 3000 rpm, runs 9mph. At 4000 (WOT), runs 9 mph. Bottom very clean. I tried new Aluminum mercury 16x12 prop. Absolutely no change.
Trim works well and is set to factory specs.
First power boat and I am lost.

 

[alldodge]

Help... I have a 1988 Celebrity 265 with 454 magnum, carburetor, bravo1 ... engine won't go over 4000 rpm and boat will not plane. Engine/drive run smooth and seems strong. 285 hrs on engine (original).
Changed plugs, cap, wires.... The boat came with a SS 16x15 prop that the previous owner changed to a new aluminum 16x14. At 2000 rpm, runs 8 mph. At 3000 rpm, runs 9mph. At 4000 (WOT), runs 9 mph. Bottom very clean. I tried new Aluminum mercury 16x12 prop. Absolutely no change.
Trim works well and is set to factory specs.
First power boat and I am lost.

:welcome: to iboats

4000 rpm and only 9mph, I would have a look at the engine coupler. Ever smell anything like burning rubber.

 

[tpenfield]

+1 on the coupler, but I would also see if the boat is water logged and therefore very heavy. Prop pitch seems way low for that kind of setup. I would expect something around a 15" dia. x 19" pitch prop on that boat.

 

[Bondo]

Ayuh,.... Welcome Aboard,...... Ya did leave the trailer in the parkin' lot, Right,..??

 

[russell veldman]

The boat did set in its slip in freshwater 4 or 5 years without moving before I took possession of it. The bottom cleaned up beautifully and I could see myself and it after I power washed it. the prop is new with a new coupling so I don't think that that's the problem - its not slipping. we thought when we went with a 16x14 we are being very conservative. perhaps I went the wrong way on the props, & I should go with a 16 x16 or 16x17? The real problem seems to be that the boat just plows, it has no problem getting to 4000 rpm but maybe the tach is wrong and 4000rpm is really 48 or 4900 rpm, I'll have to check back.
with 125 gals fuel, 30 gals water and a 2 or 300 lb Gen set on board, would that make a difference?

 

[Scott Danforth]

not the prop hub, the engine coupling. (the motor must come out) The coupling is bolted to the flywheel

a 26' boat with that motor and drive combo should be hitting 45-50mph.

something is broken. I also suggest it is the coupler.


with it sitting for 4-5 years, I would also suspect that the boat is waterlogged (wet foam, etc). I would strongly suggest you get the boat weighed. I would be willing to guess you are carrying an additional #1200+ of water

 

[tpenfield]

Check to see how it sits in the water . . . If it seems to be a bit low, then check to see if the boat is full of water, wet foam, etc. All that stuff you mentioned may take a few mph off the top end, but not all that much. You can play around with some props, but even with a lower pitched prop, it should get up on plane and do mid 20 mph. Also the engine would want to over rev a bit with those low pitch props. If mechanically, everything is fine, then you may have issues with the boat itself, bottom is nice and shiny clean, so see if you can figure out how much the boat weighs or check for water retention. Sounds like you got a nice project in the works.

 

[Bt Doctur]

One more thing to check are the trim cylinders. make sure they bottom out all the way. Had an PO use egg type zincs on the rams and the drive would not tuck in to plane off.

 

[alldodge]

Your engine coupler is located in the pic below item 24



If you remove the drive and look through the gimbal bearing hole look at the rubber around the splined shaft for cracks