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IFRs are the Idle Fuel Restrictors. One for each barrel. They meter the fuel to the idle screws. The Idle Air Bleeds in the throat of the carb meter the air. Together, they provide the ratio for the idle mixture. The adjustment screws are simply a volumn adjustment.

If your adjustment screws are only 3/4 turns or so out, then the mix is usually too rich. If so, then you can either size the IFRs down or you can open up the IABs. I like to size the IFRs down first, that way I don't mess with the timing of the main circuit.

The proper way to adjust the jetting on the IFRs is to drill and tap them for jets. But what I do is to mike a bunch of strands from some 12 to 16 guage electrical wire and use pieces of that inserted in the IFRs to see what the engine likes. Quick, easy, cheap and effective.

I leave them in when I get them about right, but a guy could go back and drill and tap them for the jets.

PVCRs are the Power Valve Channel Restrictors. They are the holes under the power valve and are essentially jets. The main jets plus the PVCRs add up to the total amount of fuel being fed. Which is why you step the mains up when you block off the power valve. The mains must be larger to compensate for the PVCRs no longer flowing any fuel.

The PVCRs can be drilled larger if the main jets are stepped down or can be wired down if they are too larger and providing too much fuel. Either way, the mix overall (mains + PVCRs) usually needs to remain about the same.

Holleys, in my experience, are usually close at Wide Open Throttle. But need a lot of help in the low speeds, transitions and cruise. Which is where a street car spends most of it's time. There are many, many combinations in these circuits on any given size carb. Which is why all carb manufacturers make street and track versions of the same size carb. It is not just about mechanical or vacuum secondaries.

Track oriented carbs like the DPs, are much richer in these areas than a street carb needs to be. For one thing, a track carb isn't too concerned about cruise.

Do you have Emanuel's Holley book? You will need it. And if you are going to experiment with the IFRs, IABs, and PVCRs, you will need to get familiar with Pi x r2. That gives you the area of the holes you will be modifying. So you know how much bigger or smaller you have made the flow.

This may be the longest post I have ever made. It had better help!

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