Quadrajets had some labor pains in the birthing process and the first year of production was an unmitigated disaster. I attended one of the first technician training seminars GM offered on the carb at the their training center in Memphis, in 1966, I believe. An innovative (and unsuccessful) approach to controlling the float level was used on the first ones which included a needle valve with a rubber diaphragm incorporated that was supposed to use fuel pump pressure to assist the float in closing the valve. Those diaphragms ruptured frequently, and resulted in massive flooding. There was absolutely nothing GM could do to solve the problem, so all those carbs were recalled and replaced with ones with a conventional needle and seat. A few aftermarket fixes were tried, none of which were successful. The leaky plugs at the bottom of the float bowl could be fixed by gently peening the metal around the edge of the plug, but the best fix was to use a fuel-resistant 2-part epoxy coating that some of the carb kit vendors offered and slathering on a generous layer during a carb rebuild. Some rebuild kits also had a thick soft plastic filler block that molded itself to the shape of the well plugs and did a fairly good job of sealing seep leaks.
Most Q-jets had 23 consecutive adjustments to make during the reassembly process, with several of them affecting the accuracy of the following setting. Make a mistake early on, and errors would stack up, making performance a nightmare, particularly where automatic choke and fast idle performance was concerned. The adjustment of the tension on the air valve spring was also a very critical setting which affected the transition from primary to secondary throttle operation. A lot of the bad publicity the Q-Jet got was the result of hurried rebuilds by guys trying to beat the flat rate labor time, not the fault of the carburetor's design or operation.
Jerry
