750 vac secondary question

« **on:** August 06, 2015, 10:29:12 PM »

I want to add the secondary metering block to my 750 vac sec. it is currently running too lean for my application. What jets should I also order along with the Holley kit? I plan to get the block with the power valve. Its going on a 454; 10.5:1 comp, comp cam 270 AH, 049 heads, slightly larger SS valves, Air Gap manifold, MSD dist and box. What other carb mods should I be considering? Thanks guys, for your advice.

« **Reply #1 on:** August 06, 2015, 10:37:19 PM »

I say ditch the vac secondary 750. Put a 850 double pumper on it and call it a day.. just my .02..

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« **Reply #2 on:** August 06, 2015, 10:49:16 PM »

What he said (Aquaholic72). An be done wit it. My 2 cents

« **Reply #3 on:** August 06, 2015, 10:54:02 PM »

If 100% of people said it wont work , I would ditch it. But I have heard enough say it will work. Just gotta set it up right. Its not a racer. Its a 20.5 cruiser.

« **Reply #4 on:** August 06, 2015, 10:57:14 PM »

Quote from: el mojado on August 06, 2015, 10:54:02 PM

If 100% of people said it wont work , I would ditch it. But I have heard enough say it will work. Just gotta set it up right. Its not a racer. Its a 20.5 cruiser.

Working and working without drama are two different things.

It's this a spread bore?

If a square bore, you should be in the neighborhood of about a 76.

GT

« **Reply #5 on:** August 06, 2015, 10:57:39 PM »

Square...

« **Reply #6 on:** August 06, 2015, 10:58:24 PM »

Are you sure about a power valve in the secondary?

Just a question.

« **Reply #7 on:** August 06, 2015, 11:06:14 PM »

You tell me. Been talking to an old jet boater. He knows more than I do bout these boats. He says i can make it work. Carb Shop in Ontario says the same.

« **Reply #8 on:** August 06, 2015, 11:19:53 PM »

Here's my stand on it..take it or leave it.. if it worked, u wouldnt be trying to add a feature to the carb it never came with.. if u really wanna run it.. step up ur main jet and read the plugs again.. power valve on the secondary side is pointless imo...especially on a vac secondary carb..again just my .02..

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« **Reply #9 on:** August 06, 2015, 11:22:11 PM »

Quote from: el mojado on August 06, 2015, 11:06:14 PM

You tell me. Been talking to an old jet boater. He knows more than I do bout these boats. He says i can make it work. Carb Shop in Ontario says the same.

The thing about a power valve is that it can get convoluted when selecting jets. A power valve can make a 6 to 8 jet size size difference.

A jet boat engine makes exactly the same load at any given rpm, pretty much no matter what. If this was a 454 in a motor home, I would say your going down a good road. But on a jet boat engine, there is no need. It's a water dyno. I say no power valve, probably 76 jets, what bowls do you have? Is it s dual feed? Center hung floats?

I want to see you succeed, but this is deep tuning 101 territory.

GT

« **Reply #10 on:** August 06, 2015, 11:23:22 PM »

Center hung floats...

« **Reply #11 on:** August 06, 2015, 11:23:54 PM »

And are you saying 76 all around?

« **Reply #12 on:** August 06, 2015, 11:28:39 PM »

Quote from: el mojado on August 06, 2015, 10:54:02 PM

If 100% of people said it wont work , I would ditch it. But I have heard enough say it will work. Just gotta set it up right. Its not a racer. Its a 20.5 cruiser.

it really seams that u want the tunability of a double pumper, hence the secondary metering block instead of the plate,but u dont want the simplicity of the mechanical linkage.?..

i myself love the k.i.s.s method..

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« **Reply #13 on:** August 06, 2015, 11:34:29 PM »

77 frt 87 rr

« **Reply #14 on:** August 06, 2015, 11:35:22 PM »

Dropping $500 is not simple right now. Changing the plate to the block and installing jets: very simple. And cheap. It might not be the best. But I think it will be good. As long as I dont melt any parts I'm having a good day.

« **Reply #15 on:** August 06, 2015, 11:39:15 PM »

I got the carb cheap and brand new. I still will have less money into it had I bought a 4150 vac secondary. Which is all I'm doing.

« **Reply #16 on:** August 06, 2015, 11:51:33 PM »

K..i understand what ur trying to do.. my next question is.. when is it lean? After u make a full throttle run, shut it down and read the plugs? Or is it lean after u putt back to the launch ramp load the boat and go home? Have u tried just steppin ur primary jets up and see if it changes? Does it spit pop and act stupid when the secondarys come in?? How do you know ur secondary side is the problem? As u said its a cruiser not a racer.. just tryin to give u some cheap advise that may help..

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« **Reply #17 on:** August 07, 2015, 12:05:32 AM »

Blew the head gasket between 2 cylinders. Jets are original to carb: 70s. It would reach 4800 rpm then would drop to just above 4000. Would pop a little. More like a crackle. I would let off and bring it down to 4000. Would cruise between 3500 and 4000 nicely. New fuel filter. Fresh gas. 91 octane. 36 degrees timing. Good fuel pressure throughout: 7psi.

« **Reply #18 on:** August 07, 2015, 12:12:49 AM »

The new motor just puked the head gasket???

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« **Reply #19 on:** August 07, 2015, 12:16:55 AM »

Quote from: el mojado on August 07, 2015, 12:05:32 AM

Blew the head gasket between 2 cylinders. Jets are original to carb: 70s. It would reach 4800 rpm then would drop to just above 4000. Would pop a little. More like a crackle. I would let off and bring it down to 4000. Would cruise between 3500 and 4000 nicely. New fuel filter. Fresh gas. 91 octane. 36 degrees timing. Good fuel pressure throughout: 7psi.

I would have gone up two jet sizes on the primary side and used the lightest yellow secondary spring and let her buck.

GT

« **Reply #20 on:** August 07, 2015, 12:18:38 AM »

Yup. 2nd trip out. But probably started at the end of my first weekend out.

« **Reply #21 on:** August 07, 2015, 12:23:46 AM »

But now with a secondary metering block what is a good place to start regarding jets for primary and secondary?

« **Reply #22 on:** August 07, 2015, 12:23:50 AM »

I 100% agree with gt...except id hit the primarys with 76's...just freshend up a 750 for a stock 460 ford..put the jets back to factory settings. 70 primary side.and it wanted pop crackle and act lean.. hit it with 76's on the primary side runs great now.. alil primary jet goes along way..

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« **Reply #23 on:** August 07, 2015, 12:24:44 AM »

Quote from: el mojado on August 07, 2015, 12:18:38 AM

Yup. 2nd trip out. But probably started at the end of my first weekend out.

Your thinking the carburetor caused this?

Do you have a picture of the piston tops?

GT

« **Reply #24 on:** August 07, 2015, 12:27:20 AM »

No i do not have a pic. No damage to pistons. Chipped porcelain in spark plug near electrode.

el mojado

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