Power Valve Plug??

Old 04-22-2009, 11:59 AM
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Location: EUGENE,OR.
Posts: 3,402

Originally Posted by Tod74
just an FYI

You asked about the 81's being too big....

I looked on Holley's website and most 750 cfm 4150 's are jetted around 70 on the primaries..depending on which model it is..may have been 69 or 71 that is with a power valve so yours is 11 or 12 bigger without the PV. So you are on the fat side of the recomended increase in jet size when the PV is removed.
I have found this too be accurate too. I just replaced one that had 72's in the primaries. I have had the same issues as you describe. Although the others here are more knowledgable than I, I have found that if you are on the street at all, you will benifit from a primary PV... like someone else said, at approx 2 steps lower than inches of idle. Another thing is allowing the the idle circuts to do thier job may require more air too (by drilling small holes in the primary butterflies). Also, make sure your floats are set correctly & needle & seat is not damaged. BTW: I have found the carb I have now works fine on the street w/a secondary PV. Scooter
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Old 04-23-2009, 06:59 AM
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Posts: 28

Great info guys.....I've really applied lots of this knowledge and have got the engine ideling much better.

Best adjustment seemed to be to open the secondary idle adjustment just a bit....really pain in the butt to get to that small screw from the underside of the baseplate but I was able to get a couple of rotations out of it to move those butterflies just a tick, adding some additional air. This allowed me to back off the primary idle screws so that I could make sure I was operating on the primary idle circuits.

Now I'm moving on to the accellerator pumps. When I hit the throttle I get a little hesitation before picking up. The holley tech site says that its almost a sure bet that the squirters need to be increased. Let me run down the numbers and tell me if from your experience this is in the ball park??

Primary squirter = 25 <-- this seems low to me
Secondary = 31

Just to recap....this is an strip only bracket car running a chevy 350 +.040, approx 11.5:1 using Brodix Track 1X heads......other carb specs are below.

Model 80528-1 4150 HP - 750cfm mech double pumper
Primary jets = 81 (PV is plugged)

Really enjoying all of the learning....so if you have any thougts about those squirter sizes....love to hear them.

thanks again!
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Old 04-23-2009, 08:24 AM
Join Date: Feb 2003
Location: Louisiana
Posts: 37

Are you running a 50cc pump back and front? If not on the front I would try that first. It,ll give you a longer shot with the smaller squirter (on front) and may kill that flat spot.
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Old 04-23-2009, 09:32 AM
Join Date: Feb 2003
Location: Louisiana
Posts: 37

Jet extentions could solve that hesitation also.
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Old 04-24-2009, 10:13 PM
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"Primary squirter = 25 <-- this seems low to me "

Ok that 25 (prim) is way to small for a healthy big breathing motor like yours.
I'd start out with 32's squared (prim & sec) and go from there.
Also if you can find them, get the squirters with the long brass nozzels sticking out, they seem to work better than the stubbys.

Ditto> on the 50cc accell pump (prim) and jet extensions (sec) and don't forget to install a notched float with the extensions.
Reason being, if you don't the float has the potential to not drop down far enough because of the extensions which wont let the needle drop down far enough which in turn can hinder adequet fuel supply during hard accelleration.
Sorry for the book, I just like to let people know why rather than say just do it, it helps with the learning curve.

Goodluck, Cp[/quote]
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Old 04-25-2009, 09:07 AM
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I think 50 cc pumps would be overkill and if anything just be a bandaid fix...I had a 950HP that had 30 cc pumps front and rear and worked beautifully on a big block.

I completely agree with the squirters being way too small. Go to Holley's website and find out what came stock in that carb and start there...sounds like someone has frak'd with that thing way too much.
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