Quadrajet Replacement

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Mar 10, 2011 | 02:03 PM

#21

wcsinx

Team Owner

Joined: Mar 2002

Posts: 24,160

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Quote:

Originally Posted by 7T1vette

There's no doubt that a 'normal' 350 cid engine will not need [or use] all of the available capacity of a 750 cfm Q-Jet. But, that has nothing to do with a response that indicates a 670 cfm Holley will produce "more" power than the Q-Jet. The carb 'flow' is only as good as the intake and heads will allow. However, that isn't the contention here. I'm questioning the validity of a 670cfm Holley having more 'oomph' than a Q-Jet.....nothing more.

I hear ya, and I think we're in agreement. "Ooomph" is a difficult thing to quantify, but running a carb that's correctly sized to the application can certainly have a SOTP effect while not significantly affecting peak HP. Perhaps that is what was being referred to?

Mar 10, 2011 | 03:00 PM

#22

damoroso

Burning Brakes

Joined: May 2008

Posts: 1,116

Likes: 5

From: Middleburg Florida

Quote:

Originally Posted by Fletch'sVette

The standard vacuum gauge reads in inhg, which stands for inches of mercury, kind of the opposite of PSI.

The best way to explain it is using a tube style anemometer. So if I took a u shaped anemometer tube and had filled it with mercury and plugged one end into my carb vacuum port and the other end was left open to the atmosphere it suck the carb end to 1.5 inches higher then the atmosphere side. Vacuum is actually the absence of pressure in a system when compared to the atmosphere.

Thanks, I thought you were refering to vacuum, which I understand. However, now the rest of the statement doesn't make sense to me. The engine will only draw what it's VE allows at speed correct? So the carb is a restriction to what degree is a matter of design. It's CFM rating, as long as all carbs are measured with the same bench mark or standard can be off as far as actual CFM are concerned, but would be relative to one another. Therefore, it's difficult to see how a 670 could flow more than a 750 of any manufacturer.

Thanks for indulging me though, I think we all can agree that like anything else, personal prefrence will come into play!!

Mar 10, 2011 | 04:40 PM

#23

Duane4238

Burning Brakes

Joined: Sep 2009

Posts: 1,124

Likes: 140

From: Western New York

Regardless, some of us like our Q-jets and some of us like our Holleys. You're not going to change someone from one side of the fence to the other. We've all been through these disagreements, and nothing is ever settled or agreed upon. Amen!

Duane

Mar 10, 2011 | 09:18 PM

#24

sweeet76

Thread Starter

Burning Brakes

Joined: May 2008

Posts: 948

Likes: 1

From: pensacola fl

Sometimes I can feel it stumble or miss when starting normal from a dead stop. It almoast feels like it is not getting enough gas. I have the book by Doug Roe but I guess I'm still not sure how to adjust the fuel and air mixture screws.

Mar 11, 2011 | 08:44 AM

#25

damoroso

Burning Brakes

Joined: May 2008

Posts: 1,116

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From: Middleburg Florida

Quote:

Originally Posted by sweeet76

First, verify your timing and make sure you don't have any vacuum leaks. There are a couple quick ways to check for vacuum leaks. At operating temp, take the air cleaner off, and slowly put your hand over the primaries and see if the engine picks up any. If it does, it's a good bet you have a vacuum leak. You can also spray carb cleaner, starting fluid or even use an unlit propane torch around the base of the carb and intake fittings to see if the engine speed picks up. If it does, you found the leak...

In adjusting the idle mixture screws, remember, on the Q-jet, there is no dedicated idle circuit. It's idle/cruise so the idle mixture screws will effect the cruise too. Set the idle mixture to get the most vacuum you can, connect a guage to manifold vacuum and work from there, making sure you get both sides even. Are there any other issues with the carb or does it run well in all other situations?

Mar 11, 2011 | 06:04 PM

#26

sweeet76

Thread Starter

Burning Brakes

Joined: May 2008

Posts: 948

Likes: 1

From: pensacola fl

Actually it seems to sputter at times when starting from a dead stop and normal acceleration. I'm not even sure if the air blades on the secondaries are opening or how to check for it. Its almost like i'm trying to overthink this whole problem therefore missing out on the normal way to solve it.

Mar 11, 2011 | 06:21 PM

#27

johnt365

Drifting

Joined: Dec 2004

Posts: 1,714

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From: Austin Texas

Can you post a picture of the choke side of the carb?

Mar 11, 2011 | 07:21 PM

#28

sweeet76

Thread Starter

Burning Brakes

Joined: May 2008

Posts: 948

Likes: 1

From: pensacola fl

Actually I'm beginning to think it might be the timing and not the carb. I just drove it again and it seems to want to go but can't, if you know what I mean. I'm going to check it in the AM. I just had some new aluminum heads oinstalled and that is the only thing different.
I will post my findings and thank everyone for the help.