How to Rebuild & Modify Rochester Q Carb (S-a Design) by Cliff Ruggles

The Rochester Quadrajet carburetor was found perched atop the engine of many a classic GM performance vehicle. The Q-Jet is a very capable but often misunderstood carb. This book, How to Rebuild and Modify Rochester Quadrajet Carburetors, seeks to lift the veil of mystery surrounding the Q-Jet and show owners how to tune and modify their carbs for maximum performance. The book will be a complete guide to selecting, rebuilding, and modifying the Q-Jet, aimed at both muscle car restorers and racers. The book includes a history of the Q-Jet, an explanation of how the carb works, a guide to selecting and finding the right carb, instructions on how to rebuild the carb, and extensive descriptions of high-performance modifications that will help anyone with a Q-Jet carb crush the competition.

From the Publisher The Q-Jet is a very capable but often misunderstood carb. This book is a complete guide to selecting, rebuilding, and modifying the Q-Jet, aimed at both muscle car restorers and racers. The book includes a history of the Q-Jet, an explanation of how the carb works, a guide to selecting and finding the right carb, instructions on how to rebuild the carb, and extensive descriptions of high-performance modifications that will help anyone with a Q-Jet carb crush the competition. History Here is a 1966 Quadrajet, carburetor number 7026260. This basic design was typical of very early production carburetors. Carburetors produced in later years would appear similar externally, but many internal changes were made to make them more reliable. Operation Some models use idle air bleeds in the air horn as shown in this 1969 Pontiac casting. The idle air bleeds expose the idle fuel that has been pulled up through the idle tubes to incoming air before it proceeds down through the idle channel restriction and makes it to the base plate. Carb Selection The rear of the base plate was a common point for large vacuum fittings to operate power brakes and other accessories. The top plate has a small pressed-in tube, and the center plate base plate uses 1⁄8-inch NPT threads, common for carburetors produced through about 1974. The bottom base plate uses 1⁄4-inch NPT threads, typical of many 1975 and later carburetors Main Fuel Bowl Tools & Safety The bottom portions of the throttle-plate retaining screws are staked at the factory. This keeps them from working loose and falling into the engine, but makes removing them nearly impossible without breaking them off in the shafts. Grinding the staked portion with an air grinder armed with a carbide cutter allows for easy removal of the screws. Rebuilding Submerging the carburetor and its components in a pail of carburetor cleaner for a few hours of soaking saves a lot of time in removing heavy deposits of grease and grime from the castings. Performance Modifications Drilling small holes in the primary throttle plates adds some additional air to the engine at idle. This is usually not required if the carburetor has an idle bypass air system in place. Many early carburetors do not use idle bypass air. Drilling the throttle plates is an easy alternative to adding idle bypass air.