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Old 05-04-2012, 07:52 AM
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Holley Power Valve selection

There has been some debate over selecting the proper power valve for a Holley carb (in my case a 4160). Holley states that you obtain the vacuum reading at idle, in gear for automatics, and half it to get the power valve needed. In my case, 13" of vac means I need a 6.5 power valve. Other people on th net say that this information direct from Holley is incorrect. I've read the vac reading should be the highest steady cruise reading and then the power valve should be about 2 below that reading. The argument is that Holley's method might result in a lean spot. On the other hand I've read if that lean spot is present, its not a power valve problem (and that the Holley method is indeed correct) but rather a main jet issue. Any thoughts?

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Old 05-04-2012, 08:49 AM
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Holley's method never worked well for me. I do the cruise rpm subtract 3 or 4, that helps a little on mileage, 2 should work just fine though.

A lean spot is most likely a result of your emulsion tuning, that is assuming its limited to a small rpm. Your jets and powervalve could be correct and still leave a lean spot, this is much more well understood by weber entusiasts as their carbs almost always require emulsion tuning.
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