The following statement is not meant to 'flame' anyone, but this is what I have "sifted" from years of these 'Q-Jet vs. Holley' discussions:

Those who can rebuild carbs and tune them prefer to do so with a Q-Jet for normal street use. Those who cannot do that work (or choose not to) prefer Holley carbs.

Holley carbs are easier to work on. But, if you set up either carb correctly, they don't need to be messed with for a long time.

However, the Q-Jet is a more sophisticated carb design with better transition between idle, off-idle, cruise and WOT operation. It also is much more economical, in that it has the small primary/large secondary design AND the secondaries are airflow regulated (the more air the engine draws, the more the secondaries are allowed to open).
_______________

There! Now, all the Q-Jet naysayers can have their turn.

 

FWIW to you, I think you would be much better off with a vac. secondary carb, like a Qjet. A good one will provide excellent throttle response, easy starting (with a good choke) and good cruising manners. Put a 14" air cleaner on it and nobody knows whats there anyway.
I have 2 good Qjets, one done originally by Lars and one by a local guru. Since those rebuilds, I have ventured as far as removing the air horn to access the primary rods and jets, accelerator pump, needle and seat and float several times for various reasons. Its a little tricky getting the air horn back on but doable. You can change secondary rods and air valve adjustments from the top so secondary tuning is easy.
Since you have a manual trans, I believe, you don't need to find a carb with the throttle arm to connect to the trans cable.
Also, if you're looking for cores, don't forget that only the Chevy carbs had the fuel inlet on the side.

 

Not in this thread, I made this thread to avoid the inevitable qjet trashing that happens in every carb thread here, sure if the qjet has a con lets discuss it but bashing it across the board helps zero,
If you hate the qjet make a thread and post that.

I fully agree with you and not to put a fine a point on it we both know why qjet haters hate them....

 

FYI, Q-Jets are mechanical secondary carbs.
They have on-demand air valve plates above the secondary throttle plates; some consider this vacuum secondary operation.
Lars explains this in his paper...

Perhaps get a junker to practice on. I've had 'em apart, but never completely disassembled.
Go for it! And post your progress, with lotsa pictures!

I love this thread already...

https://www.corvetteforum.com/forums...et-photos.html

 

The13Bats,
All I can say is take pictures of it before disassembling your core. I take pictures with my cell phone, if I have a memory issue (often) I just downloaded it to the computer and bring it up on the big screen. Also, it's easy to say to get a good core, but that is becoming very difficult to find one that hasn't been apart or tortured by bubba. The last core I got cost me $100.00 and I talked the guy down from $150. It was a corvette shop and I thought I was getting a good one with the original idle plugs still in it. I was wrong!

 

I too really dig this thread,

On the mech secondary or vacuum secondary, I was under the impression the Rochester was dependant on vacuum for how much fuel it dumps on the secondary but the holley just dumps it only dictated by linkage position.

I want to get ruggles book and I plan to grab a few qjets and tear into them, I am far too OCD not to at the very least know how to adjust the thing,
I very likely will also buy a rebuilt ( by a good name ) qjet to stick on the car a baseline I know is correct, Lars doesn't sell carbs he just rebuilds what a person has so I cant go that way, I really like sean murphy I have talked to their techs on the phone and they are down to earth and seem to know their goods, but if you have one and it sucked please do say so.

 

I had no experience with carb rebuilding and I didn't trust myself even with Cliff's book so I bought a carb from e-bay to rebuild just in case I screwed up then I would still have the carb that was on the car. I called Cliff and he recommended jet sizes to compensate for my recent mods and sent me everything I would need for a total rebuild and he told me I would be fine if I had "the book". Anyway, to make a long story short I followed the book and found the Quadrajet is really a simple carb to rebuild and it is performing flawlessly. Just take your time. You can do this!

 

A professional racer once told me that the holley is "infinitely adjustable" and can supply any required A/F ratio at any throttle setting needed for competitive use. He also recommended using the qjet for all other uses.

 

It's not a big deal, the biggest hassle is the linkages. You might be surprised how simple it really is. Just pay attention to what you are doing, and it will be a piece of cake.

 

Here is a link to Lars' Q-Jet secondary operation:

https://www.corvetteforum.com/forums...wont-open.html

 

I will be watching this as I love Q-Jets. I have never rebuilt one, and the local Q-Jet guru as unfortunately passed away. RIP Mike Bush.

 

Q-Jet secondaries are "on demand". When the carb is actuated for WOT, the secondary throttle plates are completely open. The [lightly spring loaded] air valve at top is completly closed when the throttle plates begin to open. At WOT the engine wants to suck in as much air as possible, so there is lower pressure at the throttle plates. The higher pressure above the air valve tries to push it down/open. The higher the rpm, the more air is flowed through the secondaries and the further the air valve opens.

As airflow drives down through the secondary venturi, it draws fuel in through the orifices in the body of the carb. More airflow...more fuel. Again, regulated by secondary airflow. Simple, actually.

But, it only opens as far as the engine requires of it. Therein, is one of the beautiful design features of the Q-Jet; the secondaries are self-regulating. This carb can be used on any engine that can make full use of the Q-Jet PRIMARIES (once primary rods/jets and secondary rods are properly selected for that specific engine). Beyond that, the secondaries only open as needed to satisfy the engine's need for intake air.

Folks can theorize that the pressure differential on the air valve is akin to a vacuum being on the underside of it; but that is really stretching the concept of a 'vacuum-operated' secondary...especially when many Holleys have a vacuum diaphragm gizmo on their carbs just for that purpose. It is an unnecessary device, as demonstrated by the much simpler Q-Jet design.

 

so then without oversimplifying it or using exactly the correct terms, the way the Rochester qjet operates it's secondaries sound very much how the edlebrock carter operators theirs.

I still find this far better for a street engine than a mech linkage pouring loads fuel no matter how much is really needed.

So the 64 dollar question, if you didn't have a qjet core and didn't want go core hunting which company would you buy a rebuilt qjet from?

 

Jet Performance - Others can chime in with comments...

http://jetchip.com/product-category/...ock-quadrajet/

 

I would suggest buying this one, Cliff Ruggles' book "How to Rebuild & Modify the Rochester Quadrjet", and a rebuild kit from NAPA for Q-Jet P/N 7029207. Read the book, disassemble the carb, and rebuild it yourself.

http://www.ebay.com/itm/1969-Corvett...dXICSI&vxp=mtr

I think $125 is a bit high for a Q-jet core; but this one looks to be intact and pretty close to just what you need.

 

Jeff, Jet is on my list but I cant find as mush info as I can with SMI who do this to the rebuilds,

Features
•Intended for moderately modified street performance vehicles.
•All circuits will be modified and tuned to match the specifications of your engine combination, Including:
•Idle down tube(idle jet) and idle air bleed resized for smooth idle quality with performance camshafts.
•CRO(channel restriction orifice) resized for crisp off-idle and part throttle response.
•Main jet and metering rods selected for clean cruise mixture and strong part throttle response and acceleration.
•Proper metering rod power piston spring selected to match engine vacuum characteristics
•Secondary metering rods and hanger selected and high speed air bleeds resized for maximum full throttle horsepower and torque.
•Select highest quality cores for best performance and reliability
•Strip to bare metal, inspect for defects, then apply dichromate coating for brilliant gold finish.
•Strip and cadmium plate all hardware, including throttle shafts, linkage, levers, spring and screws.
•Install bushings in baseplate to eliminate any potential vacuum leaks at primary throttle shaft.
•Install APT (ADUSTABLE PART THROTTLE) to allow adjustment of part throttle and cruise speed (steady throttle, 1800-4000 rpm) air/fuel mixture in seconds without any disassembly, tuning can be done while engine is running!
•Apply epoxy to main body casting plug to eliminate common "leak down" problem associated with Quadrajets.
•Idle, transition, main, and high speed circuits modified to provided optimum fuel curve for YOUR engine
•Assembled using the highest quality components, including:
•New jets and metering rods.
•High capacity accelerator pump featuring materials that are resistant to alcohol and other additive commonly found in today's fuel
•Nitrophyl solid composite float that can't crack or sink.
•Premium quality gaskets
•High flow .130" needle and seat assembly.
•New electric choke for cold starting and drivability.
•New choke pull-off for clean, smooth warm-ups.
•1 YR warranty all parts and labor


7T1 you know3 how cheap I am and you also know buying a qjet core is a big crap shoot,

what black c3 said Is all too true,

and People give them away, so I will score a few cores to mess with but in the meantime will buy on I know is ready and right,

I emailed a few on ebay and when I ask a so called rebuilder if they do all that stuff SMI does most start saying how they are just a home hobbyist and cant do this or that and while they might make a great qjet I would never pay a hobbyist the same price a top name like SMI gets that has far more done to it.

 

The first rebuild for me was a little hard, but take good pictures especially of any relationships between components (IE accel pump to throttle linkage, the various cams and links on the choke system) and you'll be fine.

The hardest things I know of are:
* Getting the primary metering rods into the metering rod holes through the plastic spacer.
* Getting the choke link engaged onto the choke on an M4M.
* Reading Holley vs Q-Jet posts on the internet

If you were out in CA I'd come by and help you rebuild it. I've done 10+ of these in the last few years and they're easy after the first one. If you'd like to take your hand at rebuilding it yourself, I'd be happy and I'm sure the forum would be as well to help. Maybe do a picture thread when you run into trouble and we can help on the forum.

 

[QUOTE=Shark Racer;1592591222]

* Reading Holley vs Q-Jet posts on the internet

QUOTE]


Exactly... Ha!

 

On carbs: If you want to rebuild a core, buy the best core you can get.

I've looked at all the cores on eBay. NOTHING listed would be more preferable for your car's needs than that '69 carb. Most of the rest of them (under $100) are junk that you will have to purchase at least one more core carb to make a 'good' complete unit.

Do what you will. I just hope you won't be sorry...for a mere $50 difference.

 

Newer carbs (post 75?) have the APT screw that makes it easy to set idle and partial throttle settings. Plus some of the early castings are very porous and tend to have large pieces of the fuel bowl flake off. Use Lars' papers to determine what jets/rods you have and what you need. Look for carbs that have what you need. You may find a POS carb with the proper jets that you can buy cheaply and practice on.