Quadrajet for Holley swap

[heviarti]

I am currently running a quadrajet, and am having some issues. My mileage varies wildly on the same trip, by as much as 5 MPG. My secondaries take ridiculously long to active (not at all in second, 40mph in third, 55 or more in fourth). It's had a very bad manual choke conversion done, but I don't see where they could have done anything else since it didn't have the normal round thing on the side. So, no linkage for a high idle. It seems like I have to accelerate lightly and then let off before releasing the clutch, or it will die every time no matter how easily I engage it. I also get a sort of double-lurch when engaging the clutch while moving. Acceleration is also somewhat leisurely until the secondaries activate. I don't like that.
Before he died, my brother kept telling me I needed to install a holley for more airflow. He said that would fix the problem, and he had had good results with holley on all his previous builds. I bought what was billed as being a 750 along with a weiand manifold (they would not sell them separately). After a little checking, it turns out the carb is a 600. Is that even going to be enough carb for a 383? I may be able to trade with cash for a 750.
I'm starting to kick myself for not trading for an early '80s dodge with a 318... The last one of them I was in would lay rubber in all four gears bone stock with a two barrel.

 

[Georgeb]

I would stay with the Q-jet if it were me. Get in touch with @Quadrajetpower and seek some help from others on the site about setting that carb up right and you will be amazed at how well it works. There are many other factors that effect the performance of your truck that may also need to be dealt with. All I am saying is a different carb most likely wont turn your truck into an all out tire roaster. There is more that may need to be done.

 

[SlickGTP]

I'm with @Georgeb on this... I'm still learning about and tuning my Quadrajet, but it's definitely a good carb. If you think you can do the work yourself then I'd buy something like "How to Rebuild and Modify Rochester Quadrajet Carburetors" by Cliff Ruggles. That book has a lot to offer.

In regards to the choke, you can retrofit an electronic choke on it with all the other stuff you should have like the high idle cam, so that it works as intended.

 

[heviarti]

Oh no, I don't want electric. That's like asking for a failure. I just like the electric since they come in that round case that makes it easy to install a manual.
When I got the truck the manual kit was installed in such a way that the sheath was wired onto the hood brace on the firewall, and the cable was just looped through the eye in the lever on the butterfly then wound like electric fence wire. I made it a little better by making a clamp bracket that bolts on one leg of the carb flange, and setting the cable with cable stays.
This carb doesn't have that round casting with the plastic cap that makes the change over easy. I've gone to the Edelbrock performer manifold, since my boss was throwing one away. Everyone around here seems to consider the Edelbrock carbs to be a cheaply made piece of junk, and a poor imitation of the holley. I have to say, the design of the holley seems a lot cleaner.
My boss is really sold on the quadrajet, and I have seen some very hinky behavior from them as a result. He ended up buying a whole new one and still can't get the silly thing to work. I did manage to improve the situation with a fuel pressure regulator. We have since installed a high rise k&n filter with the thought it may be choking on inadequate airflow. I snaked his old one, since he was going to throw it away.
I'll probably be installing an MSD as soon as I can, since I am just stock HEI. Everyone seems to like the HEI, I really don't. It's a great big obstruction crammed against the firewall. That's probably leaving in favor of a unilite.

 

[Quadrajet Power]

Quadrajets are often thought of as junk or no good when they dont run the best. But you have to remember that each quadrajet was built for a specific application. so they dont swap around well unless they are re-calibrated. They arent generic like off the shelf carbs. Not everybody likes them but I do. Ultimately, most people can get one custom made for their ride for less than an Eddy or Holley, and get better mileage and performance.

 

[heviarti]

It's very possible this is a lesser unit. I don't know much about the history of it other than the previous owner's dead husband built it as a 383 six years ago. They deleted all of the emissions bullcrap, went with a dual exhaust, (thereby destroying the emergency brake) and may have put a cam in it. It was a friend of his that told me about the engine. Before that I just figured it was another 350.
I traded rent on my porch to the gal... And the truck is the only good thing that came of it.

 

[Greybeard]

I'll jump in to say that if the right Q-jet is found and is set up for the specific engine they do work very good. I had one on my 74 Monte Carlo with a 454. It was factory stock and with a bit of magic by a local speed shop along with some fine tuning of the distributor and some good Jackman headers it really woke that smog choked engine up. As a street racer that car was a sleeper, as a bracket racer, it was a winner.

On the other hand, a Q-jet that is not right for the application is no better than a paperweight (I have a few of them resting comfortably in my basement). I ended up with a Truck Avenger on my current truck. Not happy with it though either. I think it's too big for my engine since it's the 670 version, the 470 would be better I think. But the specs say it's the right carb nevertheless. It could also be the Offenhouser manifold I am using. Or any number of things from the heads to the cam to the pistons or distributor.

 

[80goldenburb]

Quadrajets are often thought of as junk or no good when they dont run the best. But you have to remember that each quadrajet was built for a specific application. so they dont swap around well unless they are re-calibrated. They arent generic like off the shelf carbs. Not everybody likes them but I do. Ultimately, most people can get one custom made for their ride for less than an Eddy or Holley, and get better mileage and performance.

Hell yea i like Q-jets also. Im gonna freshen it up with some new paint. For now its collecting dust, waiting to be put on a 455 Pontiac, whenever i find one....

 

[rich weyand]

The maximum cfm a 383 can pump at 5000 rpm is about 550 cfm, so you're fine.

The Qjet properly set up will be better than the Holley unless you are in a racing application.

The Qjet may be off a 350 truck, in which case it is setup internally correctly. It may be leaking fuel at the well plugs, or leaking air at the throttle pivots, or the accelerator pump could be shot. like any other carb, after 25-30 years, a Qjet needs some attention to restore its performance.

Good luck getting the MSD set up right if you already have other issues. The HEI works well, and it is probably best to leave it on until you have your other issues sorted.

 

[heviarti]

I think I can set a 6AL up without a problem; I did it on my 300 inline six. I even installed the diode to prevent run-on, since I retrofitted to a Delcotron.
David Vizard seems to always recommend a greater than engine-capable flow for better performance.
Looking at the pros and cons we have the following:
Pros:
It's currently installed on the engine.
Cons:
It's ridiculously large.
It's not built to properly accept a manual choke
It's not repeatable
It requires a spacer to clear the air cleaner
The activation time for the secondaries appears to be chosen arbitrarily.

 

[Georgeb]

Well it sounds like you have your mind made up then.
I still say your Q-jet is not set up correctly, they are repeatable, they are not all that big, they do not "require" a spacer to clear the air cleaner (just need the correct air cleaner), the secondairies can be set to open whenever you want them too, you don't need a manual choke (I have successfully adapted one by fabricating my own manual linkage) but electric chokes or thermal chokes work just fine. In fact it is below zero here today and I started and drove my 78 with a thermal choke with zero issues. Also HEI is good ignition for a street truck and can be set up to work even better than stock.
Let us know how your mods turn out.

 

[heviarti]

Yet even if I rebuild this carb it may yet still be wrong. If they're so application specific, why would I rebuild the wrong thing, and put it back on? As to the choke, you should always have a manual choke. That's part of the reason my 1962 dodge was always ready to work, and my ford was not. It's nice to have something absolute; to have a control linked to something by a piece of metal. No guessing whether or not it's going to work, no fiddling with the pedal hoping the high idle catches, no worries about adequate electricity to operate an electric unit.
If this quadrajet is so repeatable, then you tell me how I can fluctuate between five and ten miles to the gallon on the same drive. I can give it the fact it seems to make decent power if you fiddle with it often enough. It just needs to deliver more power and less fiddling. It does seem to bear up my opinion of V8s, which is you can have one that runs well or reliably. You choose.

 

[Georgeb]

Yet even if I rebuild this carb it may yet still be wrong. If they're so application specific, why would I rebuild the wrong thing, and put it back on? As to the choke, you should always have a manual choke. That's part of the reason my 1962 dodge was always ready to work, and my ford was not. It's nice to have something absolute; to have a control linked to something by a piece of metal. No guessing whether or not it's going to work, no fiddling with the pedal hoping the high idle catches, no worries about adequate electricity to operate an electric unit.
If this quadrajet is so repeatable, then you tell me how I can fluctuate between five and ten miles to the gallon on the same drive. I can give it the fact it seems to make decent power if you fiddle with it often enough. It just needs to deliver more power and less fiddling. It does seem to bear up my opinion of V8s, which is you can have one that runs well or reliably. You choose.

I did choose. I like my Q-jet. No "fiddling" required.
You asked for help and opinions. You got them.

Good luck to you and your truck.

 

[PrairieDrifter]

Yet even if I rebuild this carb it may yet still be wrong. If they're so application specific, why would I rebuild the wrong thing, and put it back on? As to the choke, you should always have a manual choke. That's part of the reason my 1962 dodge was always ready to work, and my ford was not. It's nice to have something absolute; to have a control linked to something by a piece of metal. No guessing whether or not it's going to work, no fiddling with the pedal hoping the high idle catches, no worries about adequate electricity to operate an electric unit.
If this quadrajet is so repeatable, then you tell me how I can fluctuate between five and ten miles to the gallon on the same drive. I can give it the fact it seems to make decent power if you fiddle with it often enough. It just needs to deliver more power and less fiddling. It does seem to bear up my opinion of V8s, which is you can have one that runs well or reliably. You choose.

What is there to go bad on an electric choke? You have a simple power wire and that's it? Sure the mechanism may go bad at some point but I haven't heard of them being a problem. Quadrajet trumps all in my opinion and a lot of people on this forum believe that too.

 

[Greybeard]

I've had one Q-jet that worked awesome, and numerous Holleys that also worked awesome. Most troubles with carbs come from the owners. They put a too large four barrel on a stock engine, they put a double pumper on without any other upgrades to take advantage of it, they expect the carb to compensate for a weak ignition system or a poorly tuned distributor, worse yet is they don't even know how to tune the engine to work with the carb. There is nothing on an engine that stands alone, it is a team right down to the oil that is in it. Expectations are unrealistic for the most part when it comes to waking up a stock engine. But the stock lower end can and will wake up when everything that feeds it is designed to work together (within realistic limits). There is NO way putting a super high rise manifold with a mega carb on stock heads with stock pistons and a stock cam is going to get more than a yawn and a fart from that engine. Yet the blame will almost undoubtedly land on the carb.

So arguing about whether a Q-jet rated at twice the required airflow is right for a stock engine is pointless. It's true that millions of Q-jets graced millions of production auto's however, it was never intended as a performance carb, even if it can be built to act like one. It does have a lot of pluses that a Holley does not have, like fuel slosh is negligible in a q-jet, angles of attack does not affect it as much as a normal street designed Holley, six screws I believe and the q-jet is completely disassembled and the list goes on. Holley, on the other hand, makes application specific carbs these days, they got better controlling fuel slosh and they can work at extreme angles if that's your thing. BUT, the good ones require driving skill. A double pumper is foot sensitive because it's got mechanical secondaries.

For any style carb, if the engine cannot take all that it is given by the right foot it struggles to go. This is where the team comes in. Good flowing heads are mandatory, a good rough intake manifold with excellent distribution as determined by the cam is mandatory, a great way to scavenge the exhaust is way above mandatory. Using headers sized for the engine instead of 'bigger is better' is mandatory. A great ignition system helps. Even the air cleaner plays a role. After all the mandatory stuff is applied then the carb can be designed for the engine. However, little things like poorly fitting intake or exhaust gaskets can ruin the team. The wrong compression ratio for the well thought out mandatory pieces can ruin the game.

Overall, a Holley is much easier to work with, but that's only my opinion. It's like the argument of which is better, a 78 Blazer or a 78 Bronco. It all depends on who is asked.