Rochester Quadrajet Carburetor
Technical Reference Info
The Rochester Quadrajet carburetor has a small fuel bowl and it requires a steady and plentiful supply of fuel to perform its best. Our advice is to run 6-7 lb’s of fuel pressure for most combinations.
Install a mechanical fuel pressure gauge to verify fuel pressure delivered during WOT (Wide Open Throttle), its best to select the fuel pressure pickup point as close to the carburetor fuel inlet fitting as possible. For engines with a rubber fuel line connection close to the carb, you can obtain a fuel pressure gauge pickup fitting that will splice into the rubber fuel line. For engines with a solid metal fuel line an alternative and tempory solution is to drill and tap the fuel inlet fitting and install a compression fitting to hook up the fuel pressure gauge line.
At WOT the fuel pressure should remain constant, a fuel system that has dropping pressure needs to be improved, as the fuel system cannot keep up with the carburetor requirements. The fuel system starts at the fuel tank and includes, fuel pickup, rubber hoses, steel fuel lines, pump/s and regulator, before the fuel gets to the carburetor.
For engines producing over 400HP run an electric “pusher pump” close to the fuel tank to supply fuel to the stock mechanical pump. The Mallory 110 pump is excellent for this application as an external regulator is not required. If you plan on making 550HP or more use the Mallory 140 pump and regulator to feed your mechanical fuel pump.
Mechanical fuel pump return line-
Some mechanical fuel pumps have provisions for a return line back to the fuel tank. A return line helps keep the fuel cooler and because it allows the fuel pressure in the line to bleed off, it makes it easier and safer to remove the fuel line after shutting off your engine, without getting fuel on your hot engine.
Blocking the return line-
This can help increase fuel pressure on some models, so if you have borderline fuel pressure, this may help. Blocking the return line will almost always show an increase in fuel pressure at idle, but it is at WOT when we need the additional fuel. You need to verify with a fuel pressure gauge that blocking the return line was beneficial. If the gauge shows no benefit at WOT, then unblock the return line. If the gauge shows an increase in pressure at WOT, you should consider installing a return line restrictor. This will give you the WOT benefit of increased fuel pressure, but it will also allow the return line to bleed off pressure when the engine is shut off.