rich carb

[Ed Wright]

Cams like we run often causes low enough manifold vacuum to open the power valve at idle. The number on the power valve tells you at what point in manifold vacuum dropping as load goes up, it opens. If it says 85, the power valve opens, and adds fuel at 8.5” of manifold vacuum. A “45” will stay closed, and leaner, above 4.5” of manifold vacuum.

When I had my old IHRA Super Mod Camaro, it had the standard 750 cfm Holley we had to run in NHRA. Was a tad faster than an 850 on that 292”. Before I figured out the “High Speed Air Bleeds”, it was going lean at high RPM. I put a vacuum gauge on it to see if it was pulling vacuum “up there”, it was pulling 3” of vacuum in the lights. I went to a “25” Power Valve, and picked up a MPH. Bigger high speed air bleeds was a tad quicker.