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How to Rebuild and Modify Rochester Quadrajet Carburetors

Book Review

by Ryan King

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How to Rebuild and Modify Rochester Quadrajet Carburetors is where returning my Grandfather's El Camino to the road, begins.

I'd like to leave his El Camino entirely untouched — just get it running and go drive it. However, it's been sitting for nearly 30 years at this point and as you can see in the photo accompanying the Bench Racing post, "Priorities," his carb is going to need a complete restoration.

While I'm familiar with the Rochester Quadrajet, I don't know enough to execute a flawless rebuild/restoration and I expect all of the work I put into his Cruck to be perfect.

In order to perform a restoration on his Q-Jet that leaves everything as close to the way he had it as possible, I need to know all that I can about every component I'll need to perform work on.

That's why I picked up this book from CarTech.

The Book

I'm just going to come out and say it: this book is really well written.

The author, Cliff Ruggles, had been building Rochester Quadrajets for more than 25 years when this book was published back in 2006 and even has his own shop you can find at www.cliffshighperformance.com. You can tell immediately upon reading the first few pages, he clearly understands this subject matter.

Before I opened the cover, I wasn't looking for much more than an adequately written book from which to gain a basic knowledge of how to rebuild a Q-Jet. To my genuine pleasure, I found it quite eloquent, enjoyable to read, and it provided a lot of very valuable information in a very thin volume — 128 pages to be exact.

To find out what can be fit in less than 130 pages, follow along as I give you a chapter-by-chapter breakdown of what this gem has to offer:

Chapter 1: History

Early Q-Jet

While there are a lot of people with sufficient experience to be considered expert carburetor builders, I was elated to find someone so knowledgeable in the history of both the Quadrajet, itself, and its technical features. Not only that, but he obviously also has an excellent grasp of the historical events and related technological advances that caused the Quadrajet's changes over its 22-year production life.

It's rare to find someone who has this rich and nuanced an understanding of the history of the Muscle Car and its technology in relation to the events that shaped it. It's one of the things I truly enjoy about studying Muscle Cars: understanding their technological development contextually through history; the knowledge and motivations of the people that created them; the world they were created in; and the forces that shaped that world.

Along with the history of the Quadrajet, this chapter also provides insight into their numbering schema so that you can understand and identify them.

Chapter 2: How Quadrajets Work

Choke Linkage

Chapter 2 really does explain how Q-Jets work.

I mean, everything.

It covers the main body, fuel bowl vent, fuel inlet, fuel bowl float, idle/air system, primary metering system, secondary system, and choke. The entire carb is both explained and clearly illustrated with photos that show every facet of the inner workings of the Quadrajet — from top to bottom and stem to stern. If for some reason you finish this chapter and don't understand something, re-read it, because you missed it. It was there.

Chapter 3: Selecting the Right Carb

Fuel Inlet Position

The title of Chapter 3 says it all, but you might be surprised by the suggestions presented in it. For me and my project — returning my Grandfather's El Camino to the road as he had built it — my options are limited to the carburetor already on it. You, however, will find lots of solid advice for choosing the right Quadrajet for your application.

I'll leave you to read the book to find all the tasty tidbits that will allow you to select a good Q-Jet for your application, but I will say that those tidbits include information on the castings, fuel inlet, CFM ratings, linkages, vacuum fittings, and choke pull-offs, as well as advice on the use of remanufactured carbs and carb selection for high performance applications.

Chapter 4: Tools and Safety

Base Plate Bushing Installation Tool

One of the most significant areas where a lot of information on automotive repair is lacking is in the realm of tools and safety gear. If I'm lucky enough to find this information in a book, it often provides an incomplete list. Not only are these lists incomplete, but they almost never explain how the tools should be used. Not so in Chapter 4. Author Cliff Ruggles has really thought this book through and this chapter is thorough. That's especially important here because this book isn't about basic automotive repair, it's about specialized remanufacturing and modification, and that kind of subject needs very specific direction. If you're serious about digging into Q-Jets, you'll be happy you picked up this book because you'll find what you need to do it, right here.

Now that I've said all that, it also makes several recommendations I don't feel comfortable supporting without caveats. First, it mentions using cleaning disks on an angle grinder to remove gasket material and it says they won't damage mating surfaces. I can tell you from the experience of ruining the deck on the 347's block during a repair that cleaning disks will most certainly damage mating surfaces — and that engine block was cast iron, not soft aluminum. I know this is a common practice nowadays, but do so with caution or you may very well be finding yourself a new carburetor. Second, using a belt sander to flatten a baseplate and/or an air horn. I understand that is something that can be done, but I've also used a belt sander to unintentionally shave things at an angle by applying pressure incorrectly, so do it with extreme caution and be aware it could mean ruining your baseplate or air horn — and finding yourself a new carburetor. Third, it describes an option to use a self-guided drill bit in a hand drill on the baseplate to open up the throttle shaft bosses so that bronze bushings can be installed. I've never drilled out a carburetor baseplate before, but I have attempted to enlarge a number of openings for bushings/and or Heli-Coil inserts and found myself making oblong holes and/or drilling them at an improper angle. Again, be warned and be careful — or you may find yourself shopping for a new carburetor. I'm not saying these methods can't be used or used successfully — the author has a lot more experience than I likely ever will — but I've managed to screw up every single one of these procedures in the past, so my advice is to proceed with extreme caution if you proceed with them at all.

Chapter 5: Rebuilding the Carb

Ready for Assembly

Now we're into the meat and potatoes of the book — at least for me. Obviously with my reason for reading this book — restoring the carburetor in my Grandfather's El Camino — knowing how to rebuild a Quadrajet is critical and this chapter doesn't disappoint.

Chapter 5 starts out hitting hard right away by meticulously describing the most complex repair procedures — those that go well beyond gasket replacement but that the other books I've read on carb rebuilding have never discussed: leaking plugs, warped castings, stripped inlet threads, and loose throttle shafts.

The next two sections dig into the nitty gritty of disassembling the carb and cleaning it. This is where the special Rochester details really start coming to the fore. You'll find tips for properly removing intricate components and hard to budge pieces, as well as how to do the little things that make a Quadrajet "new" again — rather than just re-gasketed. This is the kind of information every book on rebuilding carburetors should have.

Now the section on the base plate: It does an excellent job of explaining what to do to rebuild the base plate and why it should be done — it doesn't provide any details for how to go about indexing the throttle shafts or aligning the throttle butterflies, nor does it provide any specifications for the latter. It also discusses how to modify the compression springs on the idle mixtures screws for use with drilled out idle mixture holes, but not how to drill the holes. Thankfully, all of this missing information is available in the next chapter.

One odd, but important piece of information to know, is that the section for the base plate includes descriptions of how to perform procedures on the main body, as well — like honing the power piston and accelerator pump bores. Another main body issue it addresses is how to clean out and enlarge the bores between the main and secondary fuel wells. From there, the base plate section finishes the assembly of the main body with very detailed instructions.

The air horn section is straightforward and explains how to refurbish and assemble the air horn subassembly, then fit it onto the rest of the carb.

The final section covers carburetor rebuild kits and is really eye-opening — it will help you make the right choice when choosing one for your carb.

Chapter 6: High-Performance Modifications

Secondary Accelerator System

At 29 pages, Chapter 6 is far and away the largest chapter in the book — which is a good thing because the subject it covers is both broad and detailed.

I've long known Rochesters struggle with mods — or rather, known people who struggled modding them. After reading about the high-performance modifications in this chapter, I have a pretty solid idea why.

Sure, Holleys can get complicated to tune — especially part-throttle drivability in some applications — but nothing like this. From what I've read in How to Rebuild and Modify Rochester Quadrajet Carburetors, Cliff Ruggles massages just about everything in these carbs to get them high-performance-friendly. Here's a list:

  • Base plate (and main body mods related to the base plate)
  • Idle system
  • Main metering system
  • Power pistons
  • Accelerator pumps
  • Fuel inlet seats
  • Floats
  • POE (pull-over enrichment system)
  • Secondaries (I mean everything)
  • Choke pull-offs
  • Booster rings (for large displacement, high-horsepower race-only, marine, and heavy-towing applications)

That isn't all, folks. He also provides three "recipes" as starting points for tuning engines based on their displacement, power output, and idle characteristics.

For me, at this point, I'm not certain how much of this chapter I'll be applying to my Grandfather's Q-Jet simply because the base carburetor recipe Riggles recommends is for a mild 350 and the 283 in the El Camino isn't even that: it's teensy-weensy, mostly stock with a slight bump in compression, a mild custom exhaust, and, of course, the Quadrajet feeding it.

However, if modding Quadrajets in Muscle Cars is your thing and you thought that was limited to main jets, metering rods, power pistons, and accelerator pumps, this chapter will be an eye-opener for you — and you shouldn't miss it.

Chapter 7: Edelbrock Q-Jets

Edelbrock Quadrajet Secondary Air Valve

Although Chapter 7 is short, after reading Chapter 6, it's jarringly-so, but thankfully it doesn't need a lot of space. It covers the 850 CFM Edelbrock Performer RPM Q-Jet that is no longer in production, but was developed for use with large displacement Edelbrock Performer RPM engine combinations over 450 horsepower.

After having read the rest of How to Rebuild and Modify Rochester Quadrajet Carburetors, I found an entirely new appreciation for the Performer RPM Q-Jet: It's got all the yummy bits without any of the yucky ones and if you have a need for a seriously beefed up Quadrajet for your application, this may be it — but you better like your fuel filter poking out sideways, 'cuz a straight inlet was never offered.

If you've read the rest of the book — or already have a solid understanding of the Quadrajet's systems and functions — then this chapter will give you what you need to know to use and tweak these aftermarket fuel mixers.

While reading Chapter 7, I noticed it doesn't mention the 750 CFM and 795 CFM Performer versions except in inference and at that, only in passing — which is too bad, because if the carb on the El Camino were completely toast, and I knew the Performer 750 CFM was based on the Performer RPM with all the best Quardrajet features, it sounds like it might be perfect as a replacement option.

Conclusion

Finished Q-Jet

How to Rebuild and Modify Rochester Quadrajet Carburetors is a must have for any Chevrolet nut who is still relying on a Quadrajet to motivate their Muscle Car. Of all the carbs in existence, for me, the Q-Jet has remained the most mysterious — a black box of sorts that somehow swallows technical competence and leaves behind a sense of unease because of the difficulty in rebuilding and tuning them. However, after reading this book, I no longer feel that way. Does it remove some of the last vestiges of mystery in the automotive world for me? Sure, but I've never been one to think that ignorance is bliss — and with rebuilding my Grandfather's Q-Jet in my future, knowing what I'm doing is critical — and I now have a pretty good idea of what that is. With the knowledge and illustrations throughout this book, I feel fairly confident I know enough to find myself in a heap load of trouble, but, unlike most of the time I find myself there, I've been armed with enough to know what I've done wrong and that is a rarity in automotive education — most especially enthusiast-oriented literature.

Now, there are two other sections of the book I haven't covered: Appendix A and Appendix B. They didn't warrant their own sections in this review, but they are worth mentioning before it's over. Appendix A is a list of the available secondary metering rods and their diameters at various opening degrees of the secondary air valves. Appendix B is an anatomical breakdown of the Quadrajet's three basic sections: the base plate, main body, and air horn — at least for late model carbs. I think you'll find both invaluable.

So, is there anything I would have liked to have seen that wasn't included? Yes, but nothing you would expect to find in a book about rebuilding carburetors. Because it's mentioned in Chapter 4, a tutorial on how to plate a Quadrajet would've been nice. It would also have been nice to know what finishes go on what components.

Really, though, that's just nit-picking, because author Cliff Ruggles did one heck of a job writing How to Rebuild and Modify Rochester Quadrajet Carburetors and it is simply the most exhaustive book on carb rebuilding I've ever read and I couldn't recommend it more.

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For more information contact CarTech, Inc on the web at www.cartechbooks.com, by phone 1.800.551.4754, or by email at info@cartechbooks.com.

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