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View Full Version : Need Holley Refresher course on power valves



55 Tony
10-13-2018, 06:32 PM
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?

Rick_L
10-13-2018, 07:22 PM
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.

55 Rescue Dog
10-14-2018, 06:06 AM
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.

55 Tony
10-14-2018, 01:25 PM
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. :)

55 Tony
10-14-2018, 01:32 PM
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.

Rick_L
10-14-2018, 02:58 PM
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.

55 Tony
10-14-2018, 06:33 PM
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.

55 Tony
10-15-2018, 03:33 PM
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?

markm
10-16-2018, 07:37 AM
Something is wrong here I run a 1050 Dominator on a 13-1, 454 without power valves [not drilled for them]on factory 88 jets.

Rick_L
10-16-2018, 08:58 AM
A guy on the other board last week had the backward problem - his was too rich especially at cruise. Turns out he had an air leak on an idle mixture screw. Don't know the ins and outs of that, but carefully check everything so that you know nothing is leaking that shouldn't be or plugged when it shouldn't be. Pay particular attention to the air bleeds on the top of the carb.

55 Tony
10-17-2018, 04:05 AM
Something is wrong here I run a 1050 Dominator on a 13-1, 454 without power valves [not drilled for them]on factory 88 jets.

Yes odd indeed. Although we are talking about the secondaries of a spreadbore.

Do you use the jet extension tubes? Should I?

55 Tony
10-17-2018, 04:10 AM
Rick, I checked the air bleeds and they are all clear. The plugs read well except one was dark, but when I put it back in it broke in half so it may have been cracked.

markm
10-17-2018, 06:21 AM
Yes odd indeed. Although we are talking about the secondaries of a spreadbore.

Do you use the jet extension tubes? Should I?

The only thing I have ever extended is the vent tubes in top.

Rick_L
10-17-2018, 06:40 AM
A miss can mess up the wide band reading because you now have unburned fuel and excess oxygen in the exhaust even when the mixture is correct. It's possibly going to show lean rather than rich.

On the vent tube extensions, they are always a good idea, especially if you run a hood scoop. As for jet extensions, you need them in the rear if the vehicle accelerates hard enough to push the fuel back in the bowl. This probably isn't happening on a street driven car like yours. I would think you'd need to have 60' times around 1.25 sec (or the potential for that) to need the extensions. Also the small extensions that fit in the counterbore of the jet are not my preferred way, rather I use a piece of 3/8" steel fuel line, and a plastic float that's either made with notches for the extensions or home done notches with epoxy to seal up the notch.

55 Tony
10-17-2018, 07:32 AM
The only thing I have ever extended is the vent tubes in top.

I'm really sorry to hear that! Oh, on your carb, nevermind. :)

I already have tall vents for another reason that I won't mention because I don't want to start a debate about it.

55 Tony
10-17-2018, 07:50 AM
As for jet extensions, you need them in the rear if the vehicle accelerates hard enough to push the fuel back in the bowl. This probably isn't happening on a street driven car like yours. I would think you'd need to have 60' times around 1.25 sec (or the potential for that) to need the extensions.

So far my best 60' was 1.647 Does that time start at the green light or when the wheels break the beam or whatever sensor?

markm
10-17-2018, 08:23 AM
Your time starts when your front tires clear beam.

In addition, I remove the rear piss whistle if so equipped, if a car launches hard it can cause issues.

55 Tony
10-17-2018, 10:26 AM
I have no clue whatsoever as to what a rear piss whistle is. I even googled it and learned that piss whistling is a practice of making a horse piss on command (with a certain frequency whistle). Less weight for racing. I just can't make the connection?

Do all times start then?

markm
10-17-2018, 11:49 AM
I have no clue whatsoever as to what a rear piss whistle is. I even googled it and learned that piss whistling is a practice of making a horse piss on command (with a certain frequency whistle). Less weight for racing. I just can't make the connection?

from Jegs

Holley Fuel Bowl Vent Baffle Whistle style
part #510-26-89


Do all times start then?
Yes, except reaction it starts when green light comes on.