Holley street carbs and OEM replacement units use piston- type or diaphragm- type accelerator pumps. Piston pumps don’t offer quite as positive a seal as diaphragm-typepumps. And when they’re activated, some amount of fuel always leaks out of the chamber between the piston cup and the chamber cylinder wall. Eventually,…
Fuel is quite heavy compared to air. Remember that the only thing that keeps it well vaporized at idle is the high manifold vacuum produced by the closed throttle plate. But when you open the throttle abruptly to accelerate from idle, manifold vacuum drops to zero. Also recall that the…
Power Valve Restrictions Holley carburetors for the street -especially those manufactured for 1973 and later engines with EGR systems -use two-stage power valves (see illustration). Staged powervalves open partially at one vacuum level, then open fully when manifold vacuum falls to a lower level. The first stage in these valves…
The Holley 1940 power system consists of a power valve that sits at the bottom of the float bowl. A vacuum piston sits in the bowl top which is fed with vacuum that comes up from the throttle body. At idle or low power, the intake vacuum is at it’s…
Main Jet 1920 Carburetor Kits