Holley 94 power valve

[48 Special]

I recently bought a race car that was built in the mid 1950s, it has a flat top V8 with twin Holley 94 carburetors. The front carby was leaking fuel into the barrel on idle. When I stripped the carby I found that the power valves have been modified, the guts of it have been removed and a screw inserted to block it off.
The first of many questions, Why? Why would you block off the power valve? Could it be to stop over fueling issuses?
Apart from running rich the car runs well it does not lack power, hard to start as it does not have chokes and the float level is spot on.

Any info on what to do will be awesome

Brian

[69a]

I am in no way a carb expert, but I believe if you run more than one carburetor, you don't need the power valves. I was told this by two rebuilders, and ran two engines with 2X2 Holley 94's without power valves.

[Terry,OH]

You may have had the idle slightly high for the pump discharge nozzle to start dripping. If the engine runs well without the power valve good.
If the pump discharge continues to drip at idle, under the pump discharge nozzle is a brass needle, remove the pump discharge and gently tap the brass needle down into it's seat.
The carburetor part shown is the pump discharge nozzle and not the nozzle bar.

[petehoovie]

Originally Posted by 48 Special

I recently bought a race car that was built in the mid 1950s, it has a flat top V8 with twin Holley 94 carburetors. The front carby was leaking fuel into the barrel on idle. When I stripped the carby I found that the power valves have been modified, the guts of it have been removed and a screw inserted to block it off.
The first of many questions, Why? Why would you block off the power valve? Could it be to stop over fueling issuses?
Apart from running rich the car runs well it does not lack power, hard to start as it does not have chokes and the float level is spot on.

Any info on what to do will be awesome

Brian

[glennpm]

Bottom line is that for vacuum operated Power valves, e.g., Holley's, they must be selected based to open under load. Stromberg PVs are not vacuum operated. These are excerpts from The Techno link in my signature.

[38 coupe]

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glennpm is correct, the best carburetor tune these days is done with an O2 wideband sensor, a selection of jets & power valves, and a lot of patience.
The part circled in the first picture is the accelerator pump discharge, not the nozzle bars. If you are dripping gas out of the accelerator pump discharge at idle your float is probably too high, or something is decidedly odd.

[glennpm]

I used the vacuum gauge method to select a PV for a Holley carb on my SBC '40. I subsequently installed a wide band sensor and gauge and found the PV selection as below was on the money.

"How to Pick a Power Valve"

Choosing the right power valve for your Holley carburetor involves understanding the vacuum characteristics of your engine and selecting a valve that will open at the appropriate vacuum level. Here are some methods to help you pick the correct power valve:

Vacuum Gauge Method: Hook up a vacuum gauge to the intake manifold and note the vacuum reading at idle. Automatic transmission-equipped vehicles should be in the Drive position for this test. Divide the vacuum reading by two to determine the correct power valve number. For example, if your idle vacuum is 13 inches, you would divide by two to get 6.5, which corresponds to a power valve rated at 65.

Cruise Vacuum Method: Another method involves measuring the vacuum while cruising at a steady speed, such as 65 mph. Take the vacuum reading, divide it by two, and then add two to find the power valve rating. For instance, if your cruise vacuum is 13 inches, dividing by two gives 6.5, and adding two results in 8.5, indicating a power valve rated at 85.

Vacuum Subtraction Method: Subtract two from the idle vacuum reading to determine the power valve rating. For example, if your idle vacuum is 8 inches, subtracting two gives you a power valve rating of 6, meaning you should use a power valve rated at 65."

Glenn

[tubman]

If it really is a race car, perhaps there is a good reason the power valves are plugged, and there may be other modifications made to the carbs that are not so obvious. Proceed with caution.

Here is another interesting piece of information. I am planning on running a Navarro "Universal Dual" on the 258" 8BA in my Tub. I talked to "Charlie NY" in depth about this. He suggested I run a specific set of jets (I don't remember which now) and plugged power valves on this setup. He even sent me two sets of the proper jets and two purpose-made power valve plugs. Given his reputation, I would seriously consider keeping those plugged power valves; you may need them down the road.

Also, if your problem is a leaking carb, why would you change power valves, especially on a car that you say "runs well it does not lack power"? Fix the leak first.

[joel]

Charlie Price in Fl has modern holley power valves that are machined to seat(with gasket) in 94 carbs and have a full selection of what you need by idle vac./2 method.

[tubman]

After talking to Charlie again, I think that the plugged power valves may be the proper solution on your car. Here's what he told me : "My view on the plugged PV 2x2 issue is basically tailoring the jets size to admittedly run a bit rich on the low end and bit lean at higher speeds. A workable compromise is always achievable. Using this approach a seat of the pants diagnostic is to drive the car at freeway speeds, surging is an indicator that the next jet size or two is required."

Fix the leak first and see if you are satisfied with the way the car runs. Only then if you find a problem, do you want to get into tuning your carbs.

BTW, I feel Daytona Parts is an excellent source of carburetor components.

[flatjack9]

I've talked to Charlie several times about this situation. I prefer to run power valves so I don't run rich at lighter loads. I find this the way to go.

[glennpm]

Originally Posted by joel

Charlie Price in Fl has modern holley power valves that are machined to seat(with gasket) in 94 carbs and have a full selection of what you need by idle vac./2 method.

Good to know, thanks.

[48 Special]

Hi, thank you to everyone who posted a reply and I am so sorry for not replying sooner but sometimes life get in the way of fun. After reading everything and talking to our local go fast shop i think i will leave the power valves blocked off and sort the leaks out because it does run well. Option B is to return the carbs back to original specs of power valves and jet. So again many thanks and I will see if I can get a picture of the beast on my profile.
thanks again Brian