1971 360 question

72bluNblu said

They should definitely say something along the lines that they’re making a basic recommendation for the average user, not an “end all be all” declaration that all PV’s must be half the idle vacuum.

But they’re a big company. Lots of people that buy their carbs open the box and install the carb and if they get as far as changing the jets up or down a size or two they’re doing good.

To me, any of those basic manufacturer recommendations are a starting point for your tune, nothing more. Your car idles at 20 inHG? Well that off the shelf 6.5 PV your carb came with may not be right. Your car idles at 10 inHG? Again, probably gonna have to look at that PV. That’s all it is.

It’s not “wrong”, but it won’t be right for every application either. Just like some of the advice here isn’t right for every application.

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Once again, the power valve can open at idle but it won’t flow any fuel.

No one should be setting power valve opening from idle vacuum. That makes ZERO sense because it doesn’t have any affect on the idle and it’s not influenced by idle vacuum or anything else.

To CORRECTLY set the STARTING POINT for a Holley power valve you need to know IDLE CRUISE VACUUM because that’s where the power valve functions.

You should start power valve opening 3-4 inches below CRUISE VACUUM.

Holley knows it’s wrong to use idle vacuum as a starting point.

That’s one reason why guys have fucked up, sorry running Holley carbs.

They get the power valve opening late, so they use a massive pump shot and every time they touch the throttle it slobbers fuel into the engine when it doesn’t need it.

I can’t believe it’s 2025 and guys still say there’s more than one way to skin a cat when it comes to this. It’s crazy to perpetuate the wrong.

Idle vacuum and power valve opening have no connection whatsoever.

Do what you want but doing what you say is wrong.