Q jet power piston spring

[Alan Roehrich]

I've never found the need to eliminate the power enrichment circuit in a Rochester QuadraJet. Properly tuned, it will run cleaner and work better with the circuit operational. It really doesn't need to be made stupid like a Holley.


The power piston springs are usually color coded, the soft one to use in MOST low idle vacuum race applications is orange.


The power piston spring isn't a huge factor in an all out drag race application, UNLESS you are leaving the starting line from a dead idle.



I haven't run into any engines that will idle and not maintain enough vacuum to hold a power piston on an orange spring down.


The first question is, do you "think" the engine is running rich, or do you KNOW?


If the throttle blades are closed enough to be on the idle circuit, the power enrichment circuit isn't operating.


You can check to see if it is open by using a "coffee stirrer" to push on the top of the power piston assembly. First, without the engine running, put the stick in the primary vent tube, and find the top of the power piston assembly, you'll be able to push on it, and feel it compress. With the engine running, repeat that procedure, the piston should be at the bottom of the bore and no movement should be possible.



If it is "pulling over" you'll be able to see it, and either the float level is too high, the fuel pressure is too high and is over coming the float and needle and seat assembly, or the throttle blades are too far open.


Make certain the main well plugs are not leaking, the float level is at 5/16" or lower, the fuel pressure is not too high, the needle and seat are sealing, and that the throttle blades are not open too far. As mentioned above, in some cases a simple cure for the throttle blades being open too far is a 0.090" to 0.125" hole in the primary throttle blades.


Make sure that no one has blocked off the idle air passages, as is common with "remanufactured" carburetors.



If you own a race car with a Rochester QuadraJet, and you don't own the Doug Roe book, and the Cliff Ruggles book, you're making your life extremely hard for no reason.