[64gp4spd]

Hi, is there a thread in this section that explains how to set up the idle/mixture adjustment off the secondaries on a Holley HP950?
I looked and did not find anything?

Thanks, Rich

[Tom Vaught]

Basically you set the Primary Throttle Blade position in relation to the "window" on the Primary Transfer Slot.

You readjust the Accelerator Pump Linkage so that you have .015 -.020 CLEARANCE before bottoming out the front pump diaphragm travel. You check this with the primary
blades at wot and use a feeler gauge to assure .015" more clearance before the pump
diaphragm has no more movement.

The mixture screws on the Primary will be 1 turn to 1/5 turns out from seated.

To get the curb idle rpm you want you adjust the secondary throttle blade stop.

a) Remove the factory flat blade screw (pointing towards the intake) and install the
screw from the top side of the carb. This will allow throttle blade position changes from the top of the carb.

b) Crack the secondary blades slightly (slight daylight) before installing the carb.

Now you can set the curb idle speed using the airflow from the secondary side and leave the Primary blade adjustment exactly where it belongs.

Tom V.

By the way, the Holley 950 HP carb is actually a Holley 750 CFM carb if rated at the Holley Test Pressure used for 50 years 20.4" of water vs 28" of water used in the 1996-2000 timeframe for marketing inflated Carb CFM numbers to increase sales..

[64gp4spd]

Thanks Tom, this is helpful. I have been using this carb for 20 years and just replaced the accelerator pump's and floats, along with a Pro Form billet aluminum throttle plate to have access to vacuum port for distributor. The secondary idle screw is on the top on this baseplate. I have discussed the fact that the HP 950 is not a 950 cfm carb but closer to 780-800 with people who say, "that is way too much carb for that engine."
It is on a 463ci with Torker II and 1 inch spacer, Kauffmann 310 cfm heads and Old Faithful cam. Previously on a 421 for many years.

Thank You again
Rich

[ta man]

Great carb..almost identical to mine I have a Proform billet baseplate..great for your combo..You will find or already know the idle mixture screws are very sensitive..think in 1/12 th turns like a clock for fine tuning..I run a 50 cc pump on the front and am usually in the stock jet range..

[64gp4spd]

TA Man, what is the correct gasket to use with the Proform base plate?
The one I have has a slot across the front. I have the standard Holley
Square Bore gasket between the manifold and spacer and the one with
the slot in it between spacer and carb. Seems like I have full vacuum to
both ports in the front. Shouldn't one be ported?
Thanks

[ta man]

I use the standard gasket..just double check your ports that one is manifold and one is ported..they should be.

[Tom Vaught]

On the base of the carb if you remove it and the gasket you will see that one passage goes to a transition port. It is usually covered at idle. That is the ported vacuum location for the distributor. The other port goes to a common space and then connects to both sides of a dual plane intake for manifold vacuum. You do not want manifold vacuum signals coming from only one plenum half.

Tom V.

[JLBIII]

Originally Posted by Tom Vaught

By the way, the Holley 950 HP carb is actually a Holley 750 CFM carb if rated at the Holley Test Pressure used for 50 years 20.4" of water vs 28" of water used in the 1996-2000 timeframe for marketing inflated Carb CFM numbers to increase sales..

So does this mean a Holley 850 HP carb is actually a 650 cfm carb? Thanks

[AG]

Are new Holley 950s 950 cfm?

[Tom Vaught]

Originally Posted by JLBIII

So does this mean a Holley 850 HP carb is actually a 650 cfm carb? Thanks

NO. A generic statement like above based on 30+ years of HP carb manufacture
is just wrong.

When Holley came out with their 650, 700, 750, 800, and 850 cfm HP carbs
ORIGINALLY, the cfm values were with-in 10-15 cfm of the specific number.

Then the Holley Marketing Guys followed the other carb builders who were rating the EXACT SAME "Carb Dimensions of say a 750 DP carb: Throttle Blade Size, Venturi Size, Booster Size, etc TWO HUNDRED CFM HIGHER.

Course the numbers were accurate if the carb was flowed at 28" of water test pressure. Using the Holley Carb flow spec 20.4" of water the carb will still flow 750 cfm for a #4779 carb and 850 cfm for a #4781 carb.
NOT 650 CFM.

Holley, CARTER, ROCHESTER and even Kinsler Fuel Injection used the Flow Standard 20.4" of water used for 50+ years.

At some point you have to be aware of MARKETING CLAIMS vs OEM TESTING
SPECIFIED CONDITIONS.

But if you are after bragging rights at the drive-in, go for it guy.

a Holley carb flowed at 20.4 inches of water test pressure will flow 950 cfm if flowed at 28" of water.

20.4" of water = 1.5" of Mercury Rarely does a carb see a depression across the engine of less than 1.5" of mercury.

Tom V.

[64gp4spd]

Thank You for the replies

Rich

[JLBIII]

Thanks Tom. I didn't want to derail the op question but was curious as to the difference in advertised cfm vs actual and wondered if it was across the board marketing or just a particular instance.
As for bragging rights at the drive in, braggarts bored me 50 years ago and still do so today. :<)

JB

[Tom Vaught]

People want to sell carbs, been that way for many many years.

I have posted about how some Holley employees were asked to purchase a modified carb under their name and address back in the mid 70s. Holley would repay them for the purchases. Close to 20 carbs, if I remember right, were purchased.

All were tested on Holleys flow stands with stoddard solvent (a safe fuel for testing carbs) run thru the carb passages. Not flowed "dry", flowed exactly like the engine sees. Out of about 20 carbs THREE CARBS were very slightly better on the flow bench and engine dyno vs the out of the box sample carb also tested. The same 3 carbs.

One carb was a John Reed prepped carb, one carb was a Braswell carb, but do not remember the 3rd carb modifier.

Food for thought. REALITY VS MARKETING!!!!!!!!!!!!!!!!!!!!

And the industry is even worse today for carb knowledge.

Tom V.