Always change the base gasket when installing a rebuilt carb for it to create an air-tight seal between the carb and intake. If the carb is overtightened with the four bolts mounting it to the intake the air horn will be bent creating fuel leaks and vacuum leaks. These small diaphragms rupture after years of exposure to heat and result in the secondary air valves flopping open causing a bog.Ī couple of other problems but not common are the carb being bolted to the intake with excessive torque and fuel well plugs leaking. This small vacuum break is located on the passenger side of the carb.

It is common for this part to break preventing proper operation of the secondary air valves leading to a bog.Īnother problem associated with the secondary air valves is the vacuum secondary break. This small heart shaped plastic cam is located between the secondary air valves on the air valve shaft. This filter allows you to see if the fuel pump is working as well as if there is any debris in the fuel.Īnother problem is the cam that raises the secondary metering rods when the air valves open. The best filter to use is a glass filter connected in-line between the fuel pump and carb. This filter is not an ideal candidate since it is made of paper and can not be seen unless the filter is removed from the housing. This prevents the float bowl from filling quickly and results in poor engine performance. There are a few problems with the Rochester carbs as they get older and/or are not maintained.Ī common problem is the fuel filter inside the fuel inlet housing becomes plugged with debris from dirty gasoline. If the carb is maintained properly, it will deliver years of service. The Rochester carb is the most common carb found in GM cars and trucks from the 1960's to the mid-1980's when they were replaced by fuel injection units.

Rochester quadrajet manual 7042244