Four color coded power piston springs, allow for fine tuning of primary metering rod engagement. Great aid when tuning for a larger than stock camshaft. Engines that produce less idle vacuum will require a softer spring.
How we selected these 4 springs:
QJP built a test fixture that allowed us to vary the manifold vacuum to be able to test the rates of springs. After testing many springs we determined that these 4 power piston springs gave a nice spread to be able to accommodate the needs of engines, from stock to racing cams with greatly reduced manifold vacuum.
Yellow ---- Silver ---- Black ---- Blue
<--Weakest to Strongest Spring--->
You want to use the strongest spring possible that will NOT begin opening at idle.
Spring / Inches of Vac. / Length
Yellow: / (2-7) / 0.950"
Silver: / (4-9) / 1.020"
Black: / (5-9) / 0.950"
Blue: / (8-12) / 1.450"
Inches of Vacuum are to be used for estimates only. Condition of power piston and bore can affect and change inches of vacuum. For example the blue spring is rated at (8"-12"), the power piston begins to open/lift at approximately 12" of manifold vacuum and is fully open/lifted at approximately 8" of manifold vacuum. For most stock engines with smooth idling camshafts will use the Blue spring.
Rochester Quadrajet Carburetors (except electronic models)
Rochester Dualjet Carburetors (except electronic models)