htown81vette

I think I found out why my holley is running so rich at idle-power valve blown. I've read where you can just put a plug in place of the power valve (Holley even sells them) and just increase the jets a few sizes to compensate. I was wanting to know various opinions on whether this is a good idea or not. Bare in mind I'm kinda a newbie a tuning carbs, I'm really an EFI tuner, but decided to buy this refurbished 4175 (spreadbore) for my '81 if nothing else because I wanted to REALLY learn about carb tuning which was a little before my time.

Thanks

gkull

Plugging is not a good idea. The easiest way to determine if your power valve is blown. If you can close the front idle mix screws and your idle quality doesn't change.

Tim H

Not a good street idea.
Get someone to put in a power valve protection sleeve.
It won't blow out anymore.
Spectre Performance 2408 - Spectre Performance Power Valve Savers $5.95 out of Summit.

htown81vette

this may be a dumb question but what in blue blazes is that drill bit for?

midyearvette

there are no dumb questions, just stupid answers sometimes
keep a power valve in your carb for street use
the drill bit is needed to install the blowout protector, comes with instructions
the protector works well in 90% of the time.....good modification.....good luck....

Tim H

I don't know, what if someone ask "what are the wheels for on a car"?
But I know on this site someone would have a 6 page scientific explanation.
My answer would be, " don't worry about them they are not important"

scottyp99

That would be a pretty stupid answer, Tim........(Just bustin' your chops, Tim!)

Ya know the old saying: Ask a stupid question, get a stupid answer!


Keep it between the ditches!
Scott

scottyp99

An open power valve shouldn't have any noticeable effect on the idle circuit, your problem may lie elsewhere.


Keep it between the ditches!
Scott

gkull

Scott, I guess you have never had an open power valve or don't quite understand Holley type carbs. You are getting an open source of fuel all the time. If you had an A/F ratio meter it reads full rich all the time.

chevymans 77

May be getting a little mixed up with terminology here

a ruptured (blown) power valve will allow fuel into the manifold through the carb base.

an open power valve will not allow fuel to flow into the manifold through the base of the carb, the fuel form the open power vale flows through the main well therefore has to be drawn into the manifold by air flow through the carb.

Neal

chevymans 77

the info I found on the net indicates that this carb is a single power valve carb with 1 in the primaries and non in the secondaries. You shouldn't plug the valve in the primaries.

Neal

scottyp99

No, I've never had the misfortune of having to deal with a blown power valve, and I thought I had a pretty good grip on how Holley carbs work, but I guess not. I still don't see how the open power valve would really have much effect on the idle circuit, but it's hard to argue with experience, so I'll take your word for it. I'll have to do some studying.


Keep the shiny side up!
Scott

scottyp99

Holy crap, that didn't even occur to me! Never dealt with a blown power valve, figured it would act the same as an open valve, but thinking about it, I see your point and feel a little ashamed for not thinking of it myself. Sorry I shot my mouth off without thinking it through.


Keep the shiny side up!
Scott

chevymans 77

nothing to be ashamed about, that's the great thing about the forum, we can all learn form the experience of others.

Neal

Tim H

Figures, you gave the stupid answer.

scottyp99

I guess I deserve that!


Keep the shiny side up!
Scott

Tom454

If you choose to buy a kit for the carb, make sure it has the right value power valve in it. Some of the kits I've been getting lately have a set of "generic" parts in them and the power valve has been wrong. They are -usually- stamped.

Manuel Azevedo

Not that the OP doesn't have a blown power valve, but the inst. sheets I have for a 4175 says it has back fire protection for the power valve already built in?

htown81vette

I'm wondering if it's just not the correct power valve. It has "13" stamped on it, I'm only pulling 10 in of vacuum. If that 13 means 13 inches, the power valve could being held open. Normally I run 15-21" of vacuum, but after installing the holley, only able to get 10", and it runs pig rich, like AFR 10:1, and can't get it any leaner no matter what I do with the idle screws.

htown81vette

You may be right, it does look like it has that back fire protection thingy already on it: