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Crankster · 07-09-2021, 05:03 PM

Are those spark plugs the standard heat range? Were they removed after a highway "chop"?

Getting the correct "pump squirt" will help, as will correct jetting and power valve. It helps to know what engine manifold vacuum numbers are at steady cruise and on slight hills &c.

There is some seemingly contradictory information on how to or what power valve # to select which I attribute to the intended audience. Drag racing or semi-performance engines versus stock stock street applications.

It's important to realize that engine vacuum is the only thing holding the power valve closed. The power valve should remain closed at all times other than demand for power, acceleration, under load etc. If the wrong value is selected, or it is defective, it will constantly dribble fuel.

There is also a correction factor applied for altitude or local elevation, a PV suitable for Iowa or Kansas is not going to work for high country Colorado. Plugs are really difficult to read with modern gasoline and will ordinarily look pretty lean when they are correct. The old spark plug reading color picture charts aren't really that useful anymore.

Make sure, the power valve is not open during flat ground cruise, not even a little. Then, jet up or down as necessary.

07-09-2021, 05:03 PM	#16
Crankster Senior Member Join Date: Oct 2017 Posts: 563	Re: Holley 390 CFM Accelerator Pump Are those spark plugs the standard heat range? Were they removed after a highway "chop"? Getting the correct "pump squirt" will help, as will correct jetting and power valve. It helps to know what engine manifold vacuum numbers are at steady cruise and on slight hills &c. There is some seemingly contradictory information on how to or what power valve # to select which I attribute to the intended audience. Drag racing or semi-performance engines versus stock stock street applications. It's important to realize that engine vacuum is the only thing holding the power valve closed. The power valve should remain closed at all times other than demand for power, acceleration, under load etc. If the wrong value is selected, or it is defective, it will constantly dribble fuel. There is also a correction factor applied for altitude or local elevation, a PV suitable for Iowa or Kansas is not going to work for high country Colorado. Plugs are really difficult to read with modern gasoline and will ordinarily look pretty lean when they are correct. The old spark plug reading color picture charts aren't really that useful anymore. Make sure, the power valve is not open during flat ground cruise, not even a little. Then, jet up or down as necessary.