This is a Brief survey of the Rochester Quadrajet Carburetor.
Quadrajets were used as original equipment on many vehicles from 1965 to 1990. Over 100 million have been produced.Design The QJet is a large 4 barrel carburetor that has a small primary side for fuel economy and good emissions and a large secondary side for good performance. QJets have a maximum airflow of from 750-800 cfm. Because the secondary side of the Qjet opens according to the airflow requirements of the engine, the same basic carburetor size can be used on a large range of engine sizes. The basic 750 cfm QJet casting is used from 231 CID to over 400 CID - the big secondary air valves open only as the engine breathes. For example, on a mild 350 Chevy the air valve will never open all the way - because the motor can't use more than 600 cfm or so.M4MC type (hot air choke), M4MC Quadrajets have an integral choke and a different airhorn design; also, the throttle shafts are longer than in 4MV carbs. Starting in 1968 carb numbers were stamped on the driver's side, near the back. Identification There are three basic types of QJet: the original 4M (starting in 1965), M4M (1975 onward) and E4M (from 1979). All QJets had automatic chokes, of which there are two basic types - integral (choke coil on the carb) and remote (choke coil on the manifold). 4MV carbs have the choke coil on the manifold and 4MC carbs have it on the side of the carb in a housing. An M4MC carb has a choke coil on the carb; and M4ME carb has the same type fo choke coil, but with an electric heater element in the choke coil.Choke parts, primary metering rods and throttle shafts are not interchangeable between 4M and M4M carbs. Unlike most other 4-barrel carburetors, the Rochester Quadrajet 4-barrel carburetor allows the throttle plates to be opened wider, making the carburetor more efficient. The Rochester Quadrajet 4-barrel carburetor also creates a better throttle response time and has a centrally-located float that gives excellent fuel control. Adjusting a Rochester Quadrajet 4-barrel carburetor is fairly simple when following these tips. Tools for Adjusting a Rochester Quadrajet 4-Barrel CarburetorThe tools required for adjusting a Rochester Quadrajet 4-barrel carburetor include a Philips screwdriver, needle-nose pliers, and carburetor cleaner. Cleaning the carburetor prevents soot or buildup from affecting the carburetor's function. Be sure to wear gloves to protect your hands while adjusting the carburetor. Having the right tools in place help you optimize the performance of a Rochester Quadrajet carburetor. Adjust the Idle Mixture ScrewsBegin on the driver's side and unscrew the idle mixture screws using a Philips or straight screwdriver in the front of the carburetor until the RPM starts to drop. Turn the screw out until it reaches the maximum RMP and is no longer rising. Repeat this process on the passenger side. Be sure that during this process, the screws are turned out only enough to reach the maximum RPM. Remove the Air CleanerRemove the air cleaner to inspect the top of the carburetor. If fuel is dripping, remove and clean the float and needle. Remove the top screw on the carburetor and turn the nut out. After you clean the float and needle, place the pieces back into the carburetor, taking care to adjust the float so that it contacts the needle. A carburetor adjusting tool or pliers are helpful for this step. Adjust the Air ValveLoosen the spring tension slightly on the air valve until it begins to bog down a bit. Then, bring it back up until the bog disappears. Do not open the air valve at a full 90-degree angle because it can inhibit fuel flow. Opening the valve beyond a 90-degree angle can cause a lean spot, which affects how well fuel is transported from the tubes to the carburetor. This can cause serious damage and block the flap openings.
Please note that that these are `Re-Manufactured ` which means some modifications, Accelerator linkage hook-up etc in fitting maybe required .
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