Dual Quad Carb Tuning

Takt

Member

Jul 14, 2004

48

0

6

Madison, WI

Jun 30, 2007

#1

• Jun 30, 2007

• #1

I've got a dual quad carb setup on my mustang. It is two holley carbs (390) on a high rise manifold. I've had both carbs rebuilt by a guy that knows his stuff. Before I take the car back to him, thought I was get opinions from this site.

When I get on the gas pretty hard, I have a severe hesitation. While the engine doesn't kill, it seems like it. I've read on this forum that it may be due to the squirters not being large enough to get enough fuel down to the cylinders.

So, my question. Do you agree with the need for larger squirters? Is it as simple as just changing out squirters, or do I need to thinkg about other things?

Any help would be appreciated.

Thanks, and have a great Fourth!!

 

D

D.Hearne

New Member

Sep 29, 2000

11,730

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south louisiana

Jul 1, 2007

#2

• Jul 1, 2007

• #2

Try adjusting the freeplay out of the accellerator pump arms first. It's more likely that than the squirters. Does it have a progressive linkage or do both carbs open at the same rate? The front carb should also be jetted a tad leaner than the rear to compensate for their positioning over the ports.

 

Takt

Member

Jul 14, 2004

48

0

6

Madison, WI

Jul 1, 2007

#3

• Jul 1, 2007

• #3

Both carbs open at the same time. I'll work on the accelarator arms. I'll be interested to see what can be done to get rid of the hesitation.

Thanks

tim

 

zookeeper

Founding Member

Aug 25, 2001

3,415

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109

Rogue River, Oregon

Jul 1, 2007

#4

• Jul 1, 2007

• #4

When you say "hi-rise" intake, do you mean a tunnel ram? If so those things take a ton of accel pump shot due to the extreme runner length. Low end is not one their good qualities, so whacking the throttle and expecting the car to jump right now simply won't happen. They are designed for the car to leave the line at high rpm and stay at max rpm throughout the 1/4 mile pass. Other than that, you're going to have to accept the fact that tunnel rams are not the best choice for a street manifold. They look great and I've run one on the street before, but to work on the street they need small carbs (you've already got those) a loose converter (or manual trans) and lower then normal gears. They are not totally unstreetable, but you need to be prepared to make some sacrifices in low-end power and response for the sake of a bitchin' looking manifold.

 

rbohm

Founding Member

Apr 12, 2002

6,698

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tucson,az

Jul 1, 2007

#5

• Jul 1, 2007

• #5

like zookeeper said, if you are running a tunnel ram, not good. you can use a larger pump shooter, but you will need to feed that shooter. add a 50cc reo pump as well as larger shooters if you are running a tunnel ram. if you are using an older offenhauser intake, then just go up a couple sizes on the pump shooters. another thing to look at is your ignition timing, if you dont have enough, that will also cause the engine to hesitate.

 

D

D.Hearne

New Member

Sep 29, 2000

11,730

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south louisiana

Jul 1, 2007

#6

• Jul 1, 2007

• #6

I took him to mean he had the factory OHO 2x4 intake, but I could be wrong. The Ignition timing though is one thing I hadn't thought of, good point. Lots of times what seems to be a carb issue can also be caused by ignition problems.

 

zookeeper

Founding Member

Aug 25, 2001

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Rogue River, Oregon

Jul 2, 2007

#7

• Jul 2, 2007

• #7

I'm like Hearne, when I hear the term "hi-rise" I think of a regular, aftermarket intake, the kind that usually causes slight hood clearance problems. But after seeing his avatar with the intake poking throught the hood, I suspected he and I don't have the same two-fours intake!

 

D

D.Hearne

New Member

Sep 29, 2000

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south louisiana

Jul 2, 2007

#8

• Jul 2, 2007

• #8

I don't know but seems to me a Tunnel Ram would poke out more than that. I never paid mind to his avitar before. Then again my 67 with a low riser 427 2x4 intake and 1" spacers would all barely tuck under the hood with the O.E. airfilter element in the aluminum assembly. With the filters doubled, it stuck up thru the hood but still cleared a Boss 429 hood scoop.

 

zookeeper

Founding Member

Aug 25, 2001

3,415

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109

Rogue River, Oregon

Jul 2, 2007

#9

• Jul 2, 2007

• #9

You're right, now that I take a second look. Maybe I need my eyes checked. Anyway, since he has the same carbs I have, something's not right. My throttle response from off-idle is instant. I suspect it's ignition or a tunnel ram or tall gears and a stock converter.

 

rbohm

Founding Member

Apr 12, 2002

6,698

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tucson,az

Jul 2, 2007

#10

• Jul 2, 2007

• #10

he might have spacers under the carb that push his bug catcher through the hood, or he might have spacers under the bug catcher.