Hi All,

First post here and new to jet boat community.  I bought a 1996 Hardin Caribbean open bow a few months ago and unfortunately the old owners did not have much information regarding rebuilds/pump work.  The boat runs good but there is no indication of a pump rebuild so I am thinking of having someone give it a once over after this season. 

Here is what I have gathered so far.

Engine: 454 with Holley 4010 750 CFM carb - Max RPM 4200

Pump: Berk 12JG-A - Does this mean A cut impeller?

Max MPH on my phone was 43MPH

When up on a plane the boat rides extremely low in the water, do you think a droop and or place diverter would help to get more of the boat out of the water?  Also, I am a bit confused with the different cuts of impellers; I'm guessing the motor makes around 300HP and it's max RPM is 4200.  Is the A cut impeller the best. 

Ultimately, if/when I get the pump worked on I would like a little more top speed (not sure if that is possible without more HP) and I would like to get more of the hull out of the water. 

Thanks for the help and I will post pics as soon as possible.

Yes a means a impeller and they come stock with a a impeller max u can go with a a impeller is about 55-60


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Thanks! I figured the motor was tired after all these years, but I dint think the numbers would be that drastic.  I replaced the spark plugs/wires/rotor and cap right when I bought the boat but it sounds like there could be more issues. 

4200 is a little low for a stock 454. About 265 Hp. (a stock smog 220 hp truck motor is 330 hp in a boat)
It sounds like the impeller is doing its job holding the motor back.
I would be looking at the engine and see why you cant get to about 4500 (~330hp 454) or 4800 (~400hp 454)
Things to check-
Timing
Compression check
Ignition system, dizzy, plugs and wires
Tach, accurate?
Carb and jetting (fuel quantity and quality, too)
Cam and lifters (a flat lobe or few?)

If your pump was 'loose', and needed a rebuild,  you would see an increase in rpm, and cavitation.

Dan'l

Welcome to SCJB by the way

And a smaller impeller will have less volume of water at any given rpm vs a larger cut at the same rpm (AA = overdrive, "C" cut, underdrive)

The extended chart is a little overkill for this application.

I use JBP's charts:

http://www.jetboatperformance.biz/pages/Jetdrive_Impeller_calculator.html (Thanks Tom )

Dan'l

I put that up for reference only because it was the first one I found.  For our detailed impellers, we have a proprietary chart.  The angle of the cut of our impellers is also different.  The available charts do not really apply.

The suggestion I could give, is discuss your horsepower and application with whoever will cut your impeller.  Everyone does it just a little different.

Cheers,

Joe

This gives me a place to start, I'll look into it.

Thanks!

I got my boat a few years back and it would lay down around 4200 rpm also. I found out it wasn't advancing the spark at all.. It needed a module in the distributor is all, so you might check to see if timing is advancing

Thanks for all the replies, it sounds like the motor needs some attention after this season. 

Here is a little more of what I know for sure (the boat is stored out at the river so I cant just run outside and check things out)

Carb - Holley 750 with vacuum secondaries (we just had it rebuilt so there shouldn't be any issues)

Distributor - Small cap HEI with 8 pin module, I assume its the original one.  When I changed the cap/rotor the dist looked pretty beat up so I wouldn't be surprised if there was some sort of issue. 

Can anyone recommend a shop in the OC area that is good with motor work?  Also, are most shops willing to due a test and tune out on the water.  This sounds like something that cant be diagnosed on the trailer.