The right carburetor.

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Post  bigboat on February 16th 2014, 10:09 pm

How big of a carburetor should I use on a built base 460. It 40 over roller rockers stage 3 beast cam an Rpm manifold. I’m running a 79 bronco stick 410 gears rig is set for sand. Having problems with Holley 750 double pump mechanical secondary works great wide open. Carb is in fine condition. Oh if you say AFB you should not be allowed to own tools…

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Post  dfree383 on February 17th 2014, 12:15 am

What problems are you having with the 750?
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Post  bigboat on February 17th 2014, 12:28 am

Mostly the stomp test. Clutch is out truck is rolling stomp her down she smarphs and farts wants to backfire through carb. Done matched the power valves to intake pressure there good. My guess is I need more gas.

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Post  bosshoss on February 17th 2014, 12:34 am

yup sounds like a lean stumble. try to richen the idle mixture and get some bigger shooters.... both pumps are working correct?
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Post  bbf-falcon on February 17th 2014, 3:21 am

750 isnt big enough.and yes I agree with you on the afb

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Post  dfree383 on February 17th 2014, 9:48 am

Bigger wound mKe some more power, but I'd fix what you have first, learn to tune before you get another one.
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Post  BigRigTech on February 17th 2014, 9:51 am

I ran a 750HP street on my 468, worked flawless. I had 78/88 jets in it with 3.5PV up front, blocked PV rear - foot brake car that took the stomp perfectly. Made 475HP on the dyno with a wonky/worn out duraspark dizzy. I ran a 10.85 with that carb, I'm running an 850 now and it works just as good. I will say this - my 850 doesn't like to sit long in the shop, if I don't make sure I have fuel from my front squirters before I start the engine it will give a lean backfire until I get fuel coming from them the first time. Now I pump it about 3-4 times to see the fuel before I hit the starter, it's fine for the rest of the weekend. What is your fuel pressure set at? Has the front bowl been off for any reason?
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Post  J.Toney on February 17th 2014, 12:27 pm

Timing?
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Post  supervel45 on February 17th 2014, 3:22 pm

J.Toney wrote:Timing?
I was thinking the same thing. Might want to see where it's at and play with a few different settings.

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Post  austin460 on February 17th 2014, 3:57 pm

Bigger IMO BBFs love carb.........
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Post  LivermoreDave on February 17th 2014, 5:03 pm

I willing to step out on the limb and comment. If your valve springs are not the "stage 3 beast" versions to match that "stage 3 beast" cam a well assembled and tuned 750 CFM DP will be more carb than you'll need!

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Post  HorsinAround on February 17th 2014, 5:13 pm

Are you running 50cc pumps?
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Post  IDT-572 on February 17th 2014, 6:41 pm

I just tuned a 355 Chubby this weekend doing the same thing (750 cfm double pumper). Rolling an smack the gas peddle and a bad stumble. I checked his primary and secondary squirter adjustments and both were loose. I tightened the slack up until the bolt head barely touched the pump arm and he is all smiles now.

A 750 on a 460 inch big block should never stumble............... Check timing initial and total, where it starts to advance and where it is all in at and your squirters to see if they are operational and adjusted correctly.

I have also seen the gaskets on upside down and blocking of the primary or secondary supply ports.
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Post  cool40 on February 17th 2014, 10:59 pm

another vote for timing  Question  make sure if you are useing a vac advance that its on the right vac port.if its on a "live" vac port it'll not advance....it WILL retard timing as the manifold vac drops at the hit.  Suspect 
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Post  supervel45 on February 18th 2014, 12:13 am

Sometimes people loose the checkball or needle under the squirter and it causes drainback and a similar situtation. Something to double check. Don't forget the squirter gasket either.

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