The Ultimate Guide to Holley Carburetors
Everybody has a least carburetor, but not everybody knows how to tune them, so we're giving you a bunch of charts, graphs, advice and tips so you'll know just about everything you'll need to get your carburetor tuned right.
Throttle Body
(A) Power valve vacuum port:
This connects the manifold vacuum to the power valve. This is also where newer Holley carbs are fitted with a blowout protection check ball to protect the power valve.
(B) Full manifold vacuum source:
Outlets for constant manifold vacuum.
(C) Primary throttle blades:
All air flows through these blades at part throttle up to a given percentage of throttle opening.
(D) Curb idle speed screw:
This sets the idle speed on the primary side.
(E) Secondary throttle blades:
Controlled by either mechan-ical or vacuum actuation.
(F) Secondary throttle stop:
Small adjustment screw that is a stop for the secondary throttle blades.
(G) Curb idle transfer passage:
Machine passage for idle fuel discharge to secondary side with two-port idle mixture screws for more even idle fuel entry into engine.
(H) Idle transfer slot:
This is where idle fuel enters as the primary throttle blades are opened for part-throttle operation.
(I) Full manifold vacuum source:
Outlets for constant manifold vacuum.
(J) Curb idle discharge:
This passage leads to the small hole underneath the throttle blades where the idle fuel enters the engine.
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