MTFCA Forum

On the Holley NH carburetor, why are there two idle circuit holes near the throttle plate? Seems that when the throttle is closed, the back, larger hole is on the non vacuum side side of the throttle plate and the smaller hole is on the vacuum side. Does the larger hole act an air bleed until the throttle is opened to the point where the larger hole is more influenced by the engine vacuum? Then the larger hole also provides more idle gasoline until the throttle is opened where the venturi starts to function? Thanks Mike.

The Service Bulletin explains these two holes, Extreme Idle D and Low Speed E.

Here's a little bit better copy. Volume 5, #2 — February 1924.

Thanks, Mike