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Thread: Need Holley Refresher course on power valves

  1. #1
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    Need Holley Refresher course on power valves

    I tried putting a Holley 800 spreadbore on with mixed results. The WOT is running very lean. I pulled the 94 jets and installed 99's and it only helped a little. The power valve is one of those power valve eliminators. I don't recall if that allows free flow at all vacuums, or if it restricts the flow? If it allows free flow, why is it still way lean with 99 jets?

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    If you plug the power valve you need to jet up 6-10 numbers on the Holley jet. I.e., if the carb came with 94 jets you should run 100-104 if you plug.

    Power valve should be 3-4" of mercury less than the idle vacuum reading. Example if you idle at 10" Hg you need a 6.5 power valve.

    The power valve adds fuel when the vacuum drops below the rating. If you plug you need to add fuel.

  3. #3
    Registered Member 55 Rescue Dog's Avatar
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    Wondering why you wouldn't run a power valve? It seems like an important part of the carb, unless it's only for the track, and you only run it at idle, or wide open. I would think drivability would be terrible without a power valve.

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    Quote Originally Posted by Rick_L View Post
    If you plug the power valve you need to jet up 6-10 numbers on the Holley jet. I.e., if the carb came with 94 jets you should run 100-104 if you plug.

    Power valve should be 3-4" of mercury less than the idle vacuum reading. Example if you idle at 10" Hg you need a 6.5 power valve.

    The power valve adds fuel when the vacuum drops below the rating. If you plug you need to add fuel.
    OK, thanks. I can't remember if when I ran this carb long ago if I had an A/F gauge back then. I thought I did but it doesn't look that way now. What is odd is that I just checked Holley's site and they say it came factory with 85's in the secondaries.

    I'll put a power valve in it (I have a few different ones), and sets of jets from 64 to 99. Two pair of 80's, one looks really old so I'm guessing they came out of this carb years ago.

    On a side note, after seeing how lean it was at the track, I drove home, changed jets, and went back to the track. A well lit trailer would have changed that, but this works for me being so close. Going back is mostly downhill so coasting it didn't get that warm either.
    Tony

    1955 Bel Air Sport Coupe

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    Quote Originally Posted by 55 Rescue Dog View Post
    Wondering why you wouldn't run a power valve? It seems like an important part of the carb, unless it's only for the track, and you only run it at idle, or wide open. I would think drivability would be terrible without a power valve.
    I was instructed by someone on a different group to plug it. I suppose the reason is because in normal driving it is very very rare for me to open the secondaries and not go WOT. I did drive it like that for a while and never noticed any hesitation or other problems. There is a power valve in the primary side.
    Last edited by 55 Tony; 10-14-2018 at 02:41 PM.

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    There are quite a few Holley carb models that come from the factory with no power valve. Most of those don't even have a provision in the metering block for one. I'm like you, the need for cruising AFRs with the secondaries open is not something that happens often if ever. Probably only happens with a truck pulling a load on a steep grade.

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    Quote Originally Posted by Rick_L View Post
    I'm like you, the need for cruising AFRs with the secondaries open is not something that happens often if ever. Probably only happens with a truck pulling a load on a steep grade.
    Exactly, especially with a BB.
    Tony

    1955 Bel Air Sport Coupe

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    I put a power valve in it and left the 99 size jets in it. That richened it up and it seems OK according to the a/f gauge. I assume the gauge is OK, it does spike much richer with the accelerator pump squirt like I would expect, and black smoke wasn't pouring out the exhaust. Next weekend the track is having a "diesel blowout" so I'll probably put the street tires on to test it more, like on the interstate where I can go 80mph and blend in with traffic. I also hope to weld an oxygen sensor bung in the other side just to see if both sides are equal. It does seem odd to me that it's taking jets that large, I don't know what that is a sign of when it came from the factory with 85's?

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