Does the Holley HP4150 Ultra have idle feed restrictors?

[pusherfans]

Does the Holley HP4150 Ultra have idle feed restrictors or is this a QuickFuel Ouly feature?

[StanJ]

As far as I know, all Holley carburetors have some sort of fuel metering orifice in the curb idle/transition circuit. Conventional circuitry Holley 4150/4160/2300 series carbs (not the "reverse idle" emissions-spec units, which are different animals entirely) will have them in one of three different places in the metering block:

1. In the "Y" intersection leading to the base of the idle well

2. Just underneath the idle well caps

3. In the idle circuit cross channel connecting the idle well to the face channel just in front of the idle air bleed passage (this is the default location for the Holley HP and Ultra HP carbs, as well as the QFT stuff).

Holley's 3-circuit "Dominator" carbs are also slightly different; in pre-2002 models, the idle circuit feed restriction is built into the bottom of the idle feed tube pressed into the metering block main wells, later production carbs have the idle feed restrictions in the idle circuit cross channel as with the HP Series carbs.

Now, if your question is actually about Holley carbs having replaceable "screw in" idle feed restrictions, besides the Ultra HP billet aluminum metering blocks, the the only metering block to come from Holley with them is Part# 134-276, which is a service replacement upgrade for the HP "Dorton Series" 2brls.

[pusherfans]

Originally Posted by pusherfans

Does the Holley HP4150 Ultra have idle feed restrictors or is this a QuickFuel Ouly feature?

I found my answer. (see attached) The Ultra series does have them. They use the same jets as the emulsion jets. The 4150 HP Ultra comes with .024 for the idle feed restrictors. I will try a couple sizes smaller to see if it fixes my lean to super fat rich to normal mixture issues. . .

[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

[pusherfans]

Okay, took it all apaprt. Found a problem.

The idle feed restrictors are size 32. Well, three of them say 32 and one has what looks like 42 on it and the hole is significantly bigger than the other 3

I also removed the power valve from the back metering block and installed jets 6 sizes bigger to make up for it. I was attempting to address the 3/4 throttle lean without affecting the WOT mixture, since it is fine. It had no effect on it.

Pulled the carb and cleared out all of the gas and will send it to AED Performance in the morning. I am throwing in the towel. I just don't know enough to resolve this on my own. After 2 + months, it's enough. Let's see what they can do now.

[SPF1061]

I have had great success with carbs built for me by AED. I am sure they will get you straightened out.