Fuel Inlet Orientation-
There are two variations of inlet directions on the Rochester Quadrajet main body casting, forward facing and side facing.
Fuel Inlet Filter-
The Quadrajet Fuel filter is located inside the fuel inlet. There are long and short fuel filters, depending on the length of the fuel inlet fitting. Installing a brand new filter is always advisable as a dirty fuel filter can result in a fuel flow restriction, causing fuel delivery issues. There is a spring located behind all Quadrajet fuel filters, it is used to keep the element against the inlet fitting and force the fuel through the filter media. The spring is required for the filter to work, no spring, no filtration. ( Order of Assembly- Spring is inserted in to main body casting first, then the filter is installed with open end facing forward, then inlet fitting is installed.)
Fuel Inlet Sizes-
Early Quadrajets had 7/8”-20 threads and use seal #2231 which is located at the shoulder of the inlet fitting nut. Later model Q-Jets (1972 and later) used 1”-20 threads and the seal #2232 was located at the front of the inlet fitting, sealing below the inlet threads. Both require a gentle touch during installation, as the soft metal of the carb body can easily strip. On the female thread side of the fitting can be either 5/8-18 (for 3/8" steel fuel line) or 1/2-20 (for 5/16" steel fuel line). So when you select an inlet fitting, you need to specify the correct size of both the male and female threads.
Repairing Leaking Fuel Inlet-
Worn or stripped fuel inlet threads will prevent proper tightening on the fuel inlet and will result in fuel leaking onto the intake manifold. Do not use Teflon tape on threads as pieces of tape can come loose and get hung up in needle and seat or block a metering jet. There are several repair options for a leaking fuel inlet.:
• Extended thread fittings are replacement fitting with additional threads, on slightly worn threads the extended thread fitting will reach deeper into the casting giving extra holding power.
• Self Tapping fittings are slightly oversized and will cut new, larger diameter threads in the main body casting allowing the new fuel inlet fitting to be tightened.
• O-Ring repair fittings use dual o-rings to seal against the damaged threads in the main body casting. This method works extremly well, sealing up very badly damaged threads, but the use of this repair fitting does not allow the use of a OEM in-carb fuel filter. (NO LONGER AVAILABLE)
• Heli-Coil Thread Insert- Precision formed screw thread coils of stainless steel wire is installed in the main body replacing the original threads. Thread life is dramatically increased even after repeated assembly and disassembly because the hardness of the insert. This repair allows usage of your original OEM filter and fuel inlet fitting. Note: This is not a easy operation, as the concentricity of the threads and the sealing surface must be maintained to ensure a leak free repair. We install new thread inserts and presure test the inlet threads to ensure no leaks.
Repairing Leaking Fuel Inlet Flare Fitting-
If fuel is leaking from the fuel line flare fitting, it possible that dirt or debris is trapped on the flare or the flare can fracture causing a leak. Sometimes new flare fittings may need to be ‘seated’ so they conform to the flair.
Missing Inlet Fitting Gasket-
Fuel leaking at carb inlet due to missing gasket. Early Q-Jets use a black gasket ring up against the hex nut part of the big inlet fitting as a fitting seal. Later Q-Jets use a white plastic gasket ring at the end of the fitting threads as a fitting seal. The gasket ring, not the fitting threads seal the fitting.