Does the Holley HP4150 Ultra have idle feed restrictors?

[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?

[pusherfans]

Originally Posted by 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?

I got that number from Holley directly, but they seem to be often wrong. I have an HP4150 Ultra 950 CFM. And after months of trying to dial it in, I am just about ready to try another carb. Everything is perfect, except off idle, barely cracking the throttle.

the O2 sensor (and drivability) says:

idle: 14.5-16.0
off idle, cruise, just keeping speed: 10.9-11.5
1/4 throttle: 12.5-13.5
1/2 throttle: 12.5-14.0
3/4 throttle: 14.5-16.0
WOT: 12.5-13.5

if I push the idle back to 13.5-14.5, the cruise is much richer and drives poorly, stagnates, if that's the word.....

i have already tried 8 jet sizes, 3.5 on the power valves, 78 on the air bleeds (was 68 stock) and now I was going to try the feed restrictors and after that a street carb, but I don't like the HP4150 atreet, because it lacks the adjustabilty of the secondary butterflies without removal of the carb.... i also played with multiple butterfly positions and combinations (rear closed, open, etc)

i'll pull the bowls and see what the restrictors are...


thanks for the heads up