Terms to know to make this explanation easier to understand.
Main Jet: Controls the amount of fuel that enters the Main Well of the metering block.
Main Well: The passage that carries fuel from the jets to the Boosters.
Booster: The ring that is visible when looking down the throttle bore.
Power Valve: A vacuum operated device that controls the activation of the power valve system (more on this later).
Power Valve Channel Restrictions (PVCRs from now on): Two small holes, one for each Main Well, that act like jets to control the amount of fuel delivered from the Power Valve System.
First let's start with the Power Valve itself.
A Power Valve is little more than a vacuum operated on/off switch for fuel. It operates using a vacuum diaghram and a spring, which determines when the valve opens. I believe this is best explained using an example. Let's use an engine that makes 13" manifold vacuum at idle, a typical lightly modified performer. Knowing that value, we know that a 6.5" rated power valve would be used (typical power valve selection is 1/2 the amount of vacuum at idle, in our case 13/2=6.5). So, during idle and light cruising (above 6.5" vacuum) the power valve will be in the closed position ("off"), but during moderate to full throttle operation the vacuum will drop to below 6.5" and will cause the valve to be open ("on"). The power valve itself doesn't control the amount of fuel delivered, that's the PVCR's job.
Now to the Power Valve System (PVS from now on).
The easiest way to explain the PVS is that it functions like a vacuum actuated set of jets built inside the metering block. What this means is that when the power valve is activated ("on") it will allow fuel to flow through the PVCRs into each main well (one for each main jet), on it's way to the boosters, thus making the fuel mixture "richer". This system is one of the reasons Holley carburetors are so tuneable. It allows the carb to be jetted for maximum economy / driveability, while at the same time making it possible to tune for full throttle performance without having to rely soley on the secondaries. Remember the PVCRs control the amount of fuel delivered, not the power valve.
Why does the carburetor need a PVS?
It all comes down to economy vs driveability vs performance. For the sake of simplicity, I'll leave out the secondary system and focus solely on the primary side. If there were no PVS, all of the fuel required would need to be delivered by the main jets. This is a problem because as engine vacuum decreases the need far a larger jet arises since the booster signal weakens. What this means is that if a carburetor was jetted for idle / cruising situations, the moderate / full throttle performance would suffer, and be too lean. On the other hand, if the carburetor was jetted for maximum full throttle performance it would run too rich at idle / cruise, since the higher vacuum draws a stronger signal. The PVS was designed to combat this very problem, and does it very well.
Removing (blocking) the Power Valve from the secondary block.
This is something that is very common practice among racers. The reason it works in the secondaries and not in the primary is because you never use the secondary circuit while just idling or cruising around, so the problem listed above doesn't exist. Just remember that if the secondary power valve is removed (blocked) the jets must be increased to compensate of the lack of fuel. Usually an increase anywhere from 6-10 sizes is needed, depending on PVCR size and carburetor cfm.
I didn't expect to write so much but I hope this gives a good general understanding of how the system works and why it's needed.
Very little, if any at all. The carburetor is not what makes the horse power, The rotateing system and Valve train is what makes HP.
To install power valve blowout protection on a Holley 600 carburetor, first, remove the carburetor from the engine and take off the fuel bowl to access the power valve. Then, replace the existing power valve with a blowout protection valve, ensuring it fits snugly in place. Reassemble the fuel bowl and carburetor, ensuring all gaskets are properly seated to prevent leaks. Finally, reinstall the carburetor on the engine and check for proper operation.
The PVC (Positive Crankcase Ventilation) valve typically plugs into the vacuum port on the Holley 600 cfm carburetor. This port is usually located on the front or side of the carburetor body and is designed to provide a source of manifold vacuum to the PVC system. Properly connecting the PVC valve helps to manage crankcase pressure and reduce emissions by allowing fresh air into the engine while expelling harmful gases.
To determine the appropriate power valve size for a 650 Holley carburetor, you should consider the engine's vacuum at idle. Typically, a power valve should be rated at half the engine's vacuum reading. For example, if your engine idles at 10 inches of vacuum, a power valve rated at 6.5 would be ideal. Additionally, consider your engine's performance needs and whether you're aiming for more or less fuel enrichment during acceleration.
The power valve enriches the air/fuel mixture during sudden full throttle application to prevent stumbling/sudden lean condition.
The idle speed and idle mixture are the first things to adjust and are very easy. If there is an off-idle stumble or a bog, you'll need to make adjustments to the accelerator pump and possibly the power valve to suit your engine. Here is a link to a Holley manual that explains it in detail: http://www.holley.com/data/TechService/Technical/Carburetor%20Tech%20Info.pdf
According to holley they say you can't blow the power valve now so if your car is running rich maybe the carb is too big for the engine or you need to change the jets in the front venturi's to the next smaller size.
It is in the float chamber of the carburetor.
In a Rochester 2-barrel carburetor, the power valve is typically located on the side of the carburetor body, often near the bottom. It is a vacuum-operated device that enriches the fuel mixture during acceleration or heavy load conditions. The power valve opens to allow additional fuel when the engine requires more power, enhancing performance. If you're looking to replace or troubleshoot it, access may require removing the carburetor from the engine.
first step check all the fuses under the steering column left side panel (LH drive) if the fuses are ok (there is one fuse that supply power to the idle valve and some valve for emission) check the power supply goes to the idle valve, if you dont have a tester turn on the ignition swicth then unplug and plug the connector for the idle valve, if you hear it clicking your idle vale is good. Second step take it to the carburetor expert coz several mechanics hates carburetor nowadays.
I'll give you 4. The Float System, the Fuel Jet, the Venturi Pipe and the throttle valve.
Valve. Vent, Visor, Venturi (carburetor), Vacuum solenoid valve, Vehicle speed sensor, Voltage, VIN, Valve body (transmission), Vane pump (power steering),