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nicknitro125

  • Karma: +0/-0
more speed from 12jc 460 bbf stock internals
« on: March 24, 2015, 08:46:35 AM »
New to the forum have some questions about how I can get more top end from my 19' hallett. Has a 460bbf 750cfm holley hei ignition Stock internals with a 12jc berkley w/place diverter. Turning 4200 rpm @45 mph on the gps. Just seems like I should get more speed out of my set up. Any thoughts?  Suggestions? ?
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GT Jets

  • Karma: +192/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #1 on: March 24, 2015, 08:54:14 AM »
Something sounds way off. You should be able to turn at least 4,400-4,500 rpm and the speed should touch 60 with little drama.

Tell us more about the boat and tune.

Sent from my SCH-I545 using SoCal Jet Boats mobile app

  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #2 on: March 24, 2015, 09:08:01 AM »
Boats a 77 hallett bubble deck. Runs great fires right up has awesome power curve until top end and just feels slow compared to others. And 4200 rpm seems too low to me as well. Just rebuilt the holley 750 carb and tuned it with a vacu me gauge. Not sure where my timing is at the moment but it's set to start easily and not hard crank. Pump doesn't cavitate and place diverter works great. Not sure of the impeller in the pump but it is a 12jc berkley.
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GT Jets

  • Karma: +192/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #3 on: March 24, 2015, 09:40:27 AM »
My money is on a stuck mechanical advance. You really need to know the ignition timing above 2,500rpm.

Sent from my SCH-I545 using SoCal Jet Boats mobile app

  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #4 on: March 24, 2015, 09:44:22 AM »
My guess was timing as well. The distributor is a hei with a vacume advance option but it isn't connected to the metering block on the carb like in a car or truck. Could connecting the vacume advice fix this issue? What timing should I look for at high rpm? Idle should be around 8-10 dbtdc on pump gas with stock compression if I'm not mistaken. 
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Flusher

  • Karma: +84/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #5 on: March 24, 2015, 01:11:35 PM »
Does it have and loader?  What about shoe and ride plate?  Its possible the hardware is hanging too low and creating too much drag.  Does your Place Diverter have inserts?  If so, what color insert?

Please post some pictures of the entry into the jet from the side and front.  If you have a shoe and ride plate, lay a straight edge along the keel from a few inches from in front of the intake and measure the depth of the biting edge of the shoe.  The biting edge of the shoe should be approximately even with the keel.

Its possible that you somehow ended up with a larger impeller than an A, or your engine is down on power.  Is the engine all stock?

Cheers,

Joe
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"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #6 on: March 24, 2015, 02:14:25 PM »
I'll get those pictures up soon, but as far as I know there is no type of ride plate or shoe to bite the intake water under the hull (new to jet pump terms, excuse my ignorance). But the engine is strong as ever. I'm gonna look and my set up and get some pictures up within the hour
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nicknitro125

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Re: more speed from 12jc 460 bbf stock internals
« Reply #7 on: March 24, 2015, 03:01:08 PM »
Here is the side view of the intake
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  • Karma: +192/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #8 on: March 24, 2015, 03:42:26 PM »
Here is the side view of the intake

Well that answers that.

As for the vacuum advance,  I don't think there would be much help there.

Ignition timing is different on a jet boat. Base timing and the ramp time from base to advance is somewhat irrelevant.

You should be all in (at max ignition timing) by about 2,500 rpm. A typical wot timing on a 460 is anywhere between 32° to about 38° btdc. The jeep pump does not require the torque at the bottom end like a car/truck.

Do you have a timing light?

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #9 on: March 24, 2015, 04:11:45 PM »
Yep I have a timing light that displays rpm as well so I can verify the tachometer on the boat. Gonna drop the boat in the pond here in an hour or so and I'll post my results . Gonna play with timing and record my new gps speed against current timing (unknown at moment) to proper timing ( 32-38°). Also gonna check my secondary on the carb at wot
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GT Jets

  • Karma: +192/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #10 on: March 24, 2015, 04:35:22 PM »
Yep I have a timing light that displays rpm as well so I can verify the tachometer on the boat. Gonna drop the boat in the pond here in an hour or so and I'll post my results . Gonna play with timing and record my new gps speed against current timing (unknown at moment) to proper timing ( 32-38°). Also gonna check my secondary on the carb at wot

That sounds like a game plan to me.

Start simple. Also some things to keep in mind. Fuel pressure, fuel tank venting (related to fuel pressure) and linkage adjustment  (ie reverse bucket, throttle linkage etc.)

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

sonny1717

  • Karma: +2/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #11 on: March 24, 2015, 06:18:35 PM »
Dude I have same setup in the 18ft southwind I have - it runs 65 all day with points ignition and 750 carb. It's .30 over with a mild cam. But other than that it's pretty stock. My timing  ended up around 32 degrees but my timing numbers only went to like 0-30 degrees  in the front of the motor. I made my own little white mark for reference. Good luck


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nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #12 on: March 24, 2015, 07:47:29 PM »
Well just pulled off the water, fuel pressure was good @7psi . Timing was at 18° btdc. Once I corrected the timing and set it to 32° ish. Got me a top speed of 55 on the gps. Secondary working well and all linkages fully operating.  Boat felt significantly faster and produced much more of a throaty sound. So with all that adjusted is that pretty much all I'm looking at for top speed? Now I'm thinking it must have a lower geared impeller. Was able to achieve 4600 rpm as compared to 4200 rpm .
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  • Karma: +192/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #13 on: March 24, 2015, 08:43:37 PM »
Well just pulled off the water, fuel pressure was good @7psi . Timing was at 18° btdc. Once I corrected the timing and set it to 32° ish. Got me a top speed of 55 on the gps. Secondary working well and all linkages fully operating.  Boat felt significantly faster and produced much more of a throaty sound. So with all that adjusted is that pretty much all I'm looking at for top speed? Now I'm thinking it must have a lower geared impeller. Was able to achieve 4600 rpm as compared to 4200 rpm .

Throw in 4 more degrees of timing.

She wants some lead off.

It shouldn't hurt anything. Listen for a ping.

Awesome.

GT
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

sonny1717

  • Karma: +2/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #14 on: March 24, 2015, 10:17:35 PM »
Great work dude , now your getting there 👌👌👌👌


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nicknitro125

  • Karma: +0/-0
Re: more speed from 12jc 460 bbf stock internals
« Reply #15 on: March 25, 2015, 05:36:14 AM »
Thanks for all the helpful advice. Much more prepared for parker now! 👍
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