Holley Dripping from Booster Venturi, Engine Bogs

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Apr 28, 2015 | 05:26 PM

mikem350

Thread Starter

Melting Slicks

Joined: Feb 2006

Posts: 3,105

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From: Sunrise FL

Holley Dripping from Booster Venturi, Engine Bogs

Gas dribbles out of the boosters. This only happens when coming off idle, looking down throat of carb. Engine stumbles then runs ok. Pump squirt is ok, and problem is not temp or float related.

Its a 350, stick, Dart alum heads, 225/235 roller, Victor Jr with holley 750 DP carb.
Got 72 pri jets, 6.5 power valve. 69 jets are too lean
Vac at idle is about 11-12

Does the large open plenum Victor make the carb see less vacuum...and/or is the power valve opening too soon? I bought the car this way, PO wanted a "racing" engine, and I know this part combo may not be the best. Thinking of going to 2.5 PV, need to make it more streetable.

Also want to dump the victor for a less tall dual plane manifold, hood barely clears w drop base air cleaner, suggestions?

Last edited by mikem350; Apr 28, 2015 at 06:59 PM.

Apr 28, 2015 | 05:36 PM

Jebbysan

Dr. Detroit

Joined: Mar 2012

Posts: 10,097

Likes: 4,027

From: New Braunfels Texas

Quote:

Originally Posted by mikem350

Gas dribbles out of the boosters. This only happens when coming off idle, looking down throat of carb. Engine stumbles then runs ok. Pump squirt is ok, and problem is not temp or float related.

Its a 350, stick, Dart alum heads, 225/235 roller, Victor Jr with holley 750 DP carb.
Got 72 pri jets, 6.5 power valve. 69 jets are too lean
Vac at idle is about 11-12

Does the large open plenum Victor make the carb see less vacuum...or is the power valve opening too soon? I bought the car this way, PO wanted a "racing" engine, and I know this part combo may not be the best. Thinking of going to 2.5 PV, need to make it more streetable.

And a RPM air gap dual plane...

Try a 4.5 or 3.5 power valve first......
The airgap RPM will actually make more power than a Victor Jr. if the Victor is not port matched and runner entrances blended....
Out of the box...the Victor Jr. ports are tiny.
The RPM will "signal" the carb better than the Victor....but with a stick shift...I do not believe that is what is going on here.....

Jebby

Last edited by Jebbysan; Apr 28, 2015 at 06:18 PM.

Apr 28, 2015 | 06:56 PM

Shovels and Vettes

Le Mans Master

Joined: May 2008

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2022 C3 of the Year Finalist - Modified

Oh my god, a Holley with problems? Where are all the guys now who call Quadrajets junk? What do you say now boys?

Apr 28, 2015 | 07:01 PM

mikem350

Thread Starter

Melting Slicks

Joined: Feb 2006

Posts: 3,105

Likes: 96

From: Sunrise FL

Quote:

Originally Posted by Jebbysan

So, its possible that the PV opens too soon? Was thinking of going to a 650 carb sometime also

Apr 28, 2015 | 10:59 PM

509 rat

Safety Car

Joined: Dec 2012

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I just went thrue the same thing, carb was all good inside,what it was , just to much advance in the carb, sucking fuel prematurely sucking fuel out of the boosters, flooding the moter out.tweak with your timing.

Apr 29, 2015 | 05:14 PM

Jebbysan

Dr. Detroit

Joined: Mar 2012

Posts: 10,097

Likes: 4,027

From: New Braunfels Texas

Quote:

Originally Posted by mikem350

So, its possible that the PV opens too soon? Was thinking of going to a 650 carb sometime also

A 650 DP is a nice piece on a 350 4 speed.....but this carb should work.....
Yes I believe the 6.5 is a little heavy and opening a bit too soon....
I run 4.5's in 90% of my builds if they are lower than 11-12 inches of vacuum.....
I know what Holley says.....but it almost never works out that way....

Jebby

Apr 29, 2015 | 06:15 PM

chevymans 77

Melting Slicks

Joined: May 2002

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From: Sulphur LA

St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25

The issue of fuel from the boosters is not PV related,

Hows the fuel level set, might be a little high?

Whats the idle rpm?

You have the list number for the carb?

Neal

Apr 29, 2015 | 08:35 PM

commander_47

Burning Brakes

Joined: Oct 2011

Posts: 956

Likes: 86

From: McDonough Georgia

Almost always because the float level is too high.

Next is timing

Simple fix.

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Apr 29, 2015 | 10:52 PM

509 rat

Safety Car

Joined: Dec 2012

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I agree

Quote:

Originally Posted by commander_47

Almost always because the float level is too high.

Next is timing

Simple fix.

timing and float leval.

Apr 30, 2015 | 10:55 AM

#10

Street Rat

Le Mans Master

Joined: Aug 2010

Posts: 5,339

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From: Central Texas

Check the o-ring on your needle and seat. Or change the needle and seat and set the float correctly. You are getting too much fuel in the fuel bowl imo.

Apr 30, 2015 | 02:15 PM

#11

MelWff

Race Director

Joined: May 2006

Posts: 18,710

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as others have said check the float level and check the air bleeds that they are not clogged, four small holes where booster connects to body

Apr 30, 2015 | 06:22 PM

#12

commander_47

Burning Brakes

Joined: Oct 2011

Posts: 956

Likes: 86

From: McDonough Georgia

Quote:

Originally Posted by mikem350

PO wanted a "racing" engine, and I know this part combo may not be the best. Thinking of going to 2.5 PV, need to make it more streetable.

Also want to dump the victor for a less tall dual plane manifold, hood barely clears w drop base air cleaner, suggestions?

As an afterthought, you may want to pull that carb and just check what the PO did to it.

That 750 DP is one awesome carb, but like anything, it has to be matched with the right components. Something the PO may not have done to optimum performance.

I agree that the Edelbrock is probably a better choice than that Victor. Not that the Victor isn't a good manifold, just not enough motor for that setup.

You may want to, at some point, put the carb back to stock as a starting point. Here are the stock configurations of various 750 Holley carbs.

4779 750cfm

Primary main jets 75, Secondary main jets 76, Power valve 8.5, Primary Nozzle 25, Secondary Nozzle 32

4779-1,2 750cfm

Primary main jets 70, Secondary main jets 80, Power valve 8.5, Primary Nozzle 28, Secondary Nozzle 31

4779-3 750cfm

Primary main jets 70, Secondary main jets 73, Power valve 6.5, Primary Nozzle 28, Secondary Nozzle 31

4779-4,5 750cfm

Primary main jets 70, Secondary main jets 80, Power valve 6.5, Primary Nozzle 28, Secondary Nozzle 31

4779-6,7,8,9 750cfm

Primary main jets 71, Secondary main jets 80, Power valve 6.5, Primary Nozzle 28, Secondary Nozzle 31

May 3, 2015 | 12:23 PM

#13

larrywalk

Melting Slicks

Joined: Oct 2002

Posts: 2,317

Likes: 111

From: St Louis MO

Quote:

Originally Posted by chevymans 77

The issue of fuel from the boosters is not PV related,

Hows the fuel level set, might be a little high?

Whats the idle rpm?

You have the list number for the carb?

Neal

Neal is right. The PV has nothing to do with flow at idle; it only provides enrichment while driving with a load when the intake manifold vacuum drops below its opening vacuum rating. If one substitutes a 2.5 instead of a 6.5, the engine will run lean when accelerating and vacuum is between 2.5 and 6.5" Hg.

Replace your fuel filter (in case debris is holding the needle(s) off their seats) and reset your float levels. If that doesn't work, rebuild the carb and set everything to factory specs. BTW, your combination is mild enough that the carb factory settings should be very close.

May 3, 2015 | 12:25 PM

#14

Jebbysan

Dr. Detroit

Joined: Mar 2012

Posts: 10,097

Likes: 4,027

From: New Braunfels Texas

The OP said "off idle" and the Power Valve most certainly does come into play....
If it leaks at idle only.....most likely bad or incorrectly seated metering block gaskets.

Jebby

May 3, 2015 | 12:53 PM

#15

mikem350

Thread Starter

Melting Slicks

Joined: Feb 2006

Posts: 3,105

Likes: 96

From: Sunrise FL

Fixed It!

Quote:

Originally Posted by Jebbysan

The OP said "off idle" and the Power Valve most certainly does come into play....
If it leaks at idle only.....most likely bad or incorrectly seated metering block gaskets.

Jebby

Guys, I finally nailed it! Swapped to another 750 DP carb I had and noticed the fuel flooding stopped when hot. The old carb has those nitrophyl solid plastic floats, new one has hollow. The floats were sinking. Fixed the HOT flooding problem. Ordered 2 new METAL floats!!

Next problem, gas dribbling thru the venturis above idle, bogging: Tried changing jets from 72 to 69. Bad move, went back to 72. Did a 4.5 power valve swap, and started advancing the timing. Was at 10 deg, thought I was in the ballpark. But now at 20+ deg (plus a 17 mech), car runs like it should, no bogs, drips. Even in 5th (1-1) pulls smooth from 2000 rpm.

Next I need to check actual TDC and accuracy of timing marks!! Balancer is a new ATI but maybe the tab is off. Maybe tweek the dizzy a little more too, have kit from MSD.

So, timing + floats = success!

Thanks for all the inputs

Last edited by mikem350; May 3, 2015 at 12:57 PM.

May 3, 2015 | 01:46 PM

#16

toddalin

Le Mans Master

Joined: Oct 2000

Posts: 8,897

Likes: 1,357

From: Santa Ana CA

There is a video on YouTube devoted just to the phenonom of Holley "pullover" and it actually shows fuel being pulled from the squirters under load with no throttle movement. It also discusses the remedy.

Enjoy: