This way you can see the rod and spring and will know exactly when the spring makes contact. Choke parts, primary metering rods and throttle shafts are not interchangeable between 4M and M4M carbs. Sometimes the accelerator pump bore gets glazed where it doesn't seal against the piston very well. Once the air horn is off you can knock the plug out from the inside. Loosen the allen head screw until you see the tension go completely out of the butterfly. A dual plane intake separates totally the intake runners between cylinder 1,3,5,7 and 2,4,6,8.
Admittedly, I'm a do-it-yourselfer, not a mechanic. A slotted screwdriver is used to turn the spring adjuster after you loosen the Allen screw. Also, take the time to match up the new parts with the old ones as soon as you remove them. The pump sounds like it may have failed, or may have failed prematurely due to incorrect installation. Also, there shouldn't be a noticeable transition into the secondaries. Final Calibration Upper Idle Air-Bleed 0. The power valve was opening way too early and the secondaries were too rich.
If you prefer, keep written notes as you go along. It can be carefully bent to set the opening amount. You don't want to remove the finish, just break the glaze ever so lightly and to smooth the bore. Start the engine, let it warm to normal operating temp. Don't tap all the way to the bottom of the hole, you won't the plug to sit flush, so check the depth as you are tapping the hole.
Chevy Truck Magazine This is an insert from an article on Q-jet Tuning Tips that appeared in the January 2000 issue. A good book that everyone who has a Q-jet should have is Doug Roe's Rochester Carburetors. This intake manifold requires a specific gasket and heat shield below left be used to prevent vacuum leaks and to resist the heat. There is much more to adjusting a Q-Jet than angle of throttle plates. There are different locations for the orifices, but they're all adjacent to the primary throttle bores of the baseplate. You can do this either as you are taking pictures or when you upload them to your computer. Remember, both idle mixture screws must be adjusted equally! Wiki articles and Hotrodders Knowledge Base links Wiki article intended to provide information on rebuilding a carburetor.
A Quadrajet carburettor car is often distinguishable from other cars by the sound of the engine as the secondaries open. Going beyond this can cause a lean spot as it effects how well fuel is pulled from the tubes and the lower edge of the flap nearly blocks the openings. Most performance enthusiasts shun the Quadrajet as a stock carburettor laden with useless emissions controls. A drill press is the way to do this best, with the throttle plate clamped down. This seemed to work fairly well in cool weather, but as soon as it started warming up, I started having problems.
Just enough to allow the screwdriver to turn the adjusting screw. The M4M is the emissions Q-Jet introduced in 1975, which has had certain adjustability added in while some of the off-idle power transition is taken out. For proper accelerator pump discharge Olds engines always use the inner lever arm position. 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. Enlarging a few small restrictions by drilling can increase available idle fuel and transform the Quadrajet into an excellent, low-buck alternative that can satisfy the needs of most any combination. The circuit consists of a series of fixed restrictions within the main body and a pair of mixture screws located on the throttle body.
The most important part of the rod is the power tip. Unfortunately, trying the carb on your running engine is about the only way you can know for sure, unless the desired orifice sizes are known ahead of time. The primary and secondary fuel circuits control moderate-to-heavy part-throttle and full-throttle performance, respectively. Of course, this also means heavier part-throttle load may make the engine run lean — which is not good. However, we found that removing a vacuum hose still caused engine speed to increase slightly, indicating that the engine might benefit from additional bypass air. This is the area of the rod still in the fixed jet when the air valve door is 100 percent open.
Keep things to a minimum- smoothing obvious flaws and mismatches, and leave the rest alone. The carburetor is held in place by two long bolts visible on top of the air horn and either two nuts or two bolts on the back of the carburetor on top of the throttle cable bracket. In this series of articles, I chronicle the process of modifying and rebuilding a 1978 tilt and telescoping steering column that I plan to use in my 1976 Corvette. Return to Copyright April 2011 Eugene Blanchard. If they're over tightened, it can warp the carb permanently.