[StanJ]

.024"?

You might want to double check that for your particular carb model (remember, "4150" is a series designation that covers a host of carb sizes); from my experience, that sounds extremely small...especially for Holley baseline calibrations.

Typically, idle feed restriction i.d. down in the low-to-mid .020"s is either "dual 390cfm 4brl/small displacement/small plenum tunnel ram/short duration high vacuum camshaft" territory, or older "pre-HP" 3-circuit Dominator calibration (due to the separate intermediate idle circuit used in those carbs).

I work with these things almost daily, and in my experience the "stock" idle feed restrictor sizes for the 4150 Ultra HP series carbs are as follows:

List #80674 650cfm 4brl. .036"

List #80675 750cfm 4brl. .035"

List #80676 950cfm 4brl. .037"

Note that these sizes do not progress in a linier fashion based strictly on carburetor airflow capacity. Even before throwing engine specifications into the mix, the correct idle feed restriction size for a given carb is affected by several other factors...venturi booster design, transfer slot length/position, accelerator pump calibration being just a few of them.


What size carb do you have?