Rochester Quadrajet

This is a subject that is near and dear to my heart especially since I worked for years with GM at the Rochester Products Fuel Systems plant. I grew up on the quad and its related cousins TBI (Throttle Body Injection) and MPFI (Multi Port Fuel Injection). I was privileged to travel all over this Country, Mexico and Canada supporting the product lines. I have seen more races won with guys who really understand the Quadra jet that any other 4 barrel application. Don’t get me wrong there are many fine builders of 4 barrels but the Quad is my favorite.  One I know the unit inside out and for me I can rebuild one in a heartbeat. Two: its 750CFM bores allow me to build a carb that can take into account just about any engine combination. of which GM did take advantage of. The carb could cover small blocks, low Horse Power, Trucks, Marine, Military, Police, Racing, high horse power and high torque applications, just to name a few. Understanding the Quad however can be daunting due to its variations, however I will try and demystify the issue that many find as obstacles.

 

First off, a lot of people complain that their car, boat truck etc. is not operating up to par. They also tell me that they attempted to rebuild or have someone rebuild the carb and in some cases it turned out worse. In a nut shell what many perceive as the right thing to do is the wrong thing to attempt? The biggest killer of any fuel system is cleanliness, all systems get dirty and no amount of fuel cleaner will get it all out. In carburetion this is especially true when there are tiny passages throughout. Ethanol is a gummy gooey glob that cannot be rinsed out totally by the use of additives. This is a major problem with cars and especially with boats that are in layup for an extended period of time. In many if not all marine carbs I find teaspoons of this goo in many different spots including the float bowl. However it does go beyond this, when you are rebuilding a carb the first thing is to get the right rebuild kit for your engine and application. Secondly tear the unit completely down and soak in a good quality carb cleaner. Here it is in nut shell for successful carb rebuilds.

 

1: Obtain a quality rebuild kit from a good source, matched to your application. Beware many carbs have been swapped on many engines. Check out your engine and application and find the right carb number that matches. Then check to see if the carb you have on is the right one. However don’t despair if it is not it. The beauty with Quads is the fact the many components are the same with minor variations. I have built many quads that match an application on different body numbers. This I will explain at a later date.
2: Take pictures as you tear down your unit, and soak all your parts according to your carb cleaner’s instructions. Many shops have parts cleaners, however in some cases the solvent is not strong enough to clean carbs, thus they will need longer soak times.
3: Blow out all passages and ensure that they are clear.
4: Assemble your unit in a clean space, well illuminated, and take your time.
5: Do not adjust any of the carbs settings, wind up spring, etc. bending linkages, etc. The carb came perfectly flowed from the factory. The only exception is the "Air Fuel Idle Screws", which for the most part you will find the initial settings for setting the screws. Generally you would turn them in clock wise lightly to its stop, do not force or you will run the screw and possibly the throttle plate. Back out the screws “1-1/2" turns and this will initially allow you to start.

 

There are a few other concerns about Carburetion systems regardless of manufacture. One is the fact that leakage can occur at the throttle plate where the throttle shafts pass through. This is not as common on low millage units even though it might be of an older car or boat. This type of wear is dependent on long usage. Again this is a repairable situation. See "Quad Fixes and Tricks"

Another issue is that somewhere along the line someone has cranked the carb down on to the manifold to tightly. This will in fact warp the unit and in some cases drastically. Again this is a fixable situation that can be handled by someone with some patience, one of my tricks or a shop that specializes in such work.

Any points from here, are in my next segment "Quad Fixes and Tricks"

 

For Detailed Build Sheets on GM Carbs from 1963 Thru 1980 Vist "GM Carburetor Build Sheets"