Since Holley Doesn't Make 2 Stage PV's Anymore, Should I Get a Walker 2 Stage PV or..

[qikgts]

...a Genuine Holley single stage based on the old 1/2 the idle vac reading rule of thumb?

I found a list of the Walker parts and put them below to help out here.

Mr. Cook has posted about 2 stage PV's he's measured and likes to use that open at 10.5 and 6.5. I'm guessing those were genuine Holley though. Walker has a few that are close but none right at those specs.

Without wideband tuning am I likely to notice a difference between some of the ones that are pretty close like the 70-27 and the 70-50?

They seem kind of pricey ($22.00 or so each) to buy more than 2 to test with but I really want to try to give the 2 stage jobs a whirl to see if I like the results in my stock (less duals with an x pipe) '85. Oh, and it still sports the 4180c that at this point runs pretty good but has a single stage PV that came in the Holley 3-1346 rebuild kit.

[Walking-Tall]

Votes for genuine ~1/2 manifold vacuum at loaded idle, and jetting up a few numbers in the primaries IF there is cruise or mild acceleration lean surging. It's useful to find the lean limit to know where it is anyways.
What is it doing wrong right now with a single stage in it?
The use of a 2-stage power valve was a dog'n'pony show to get away with slightly leaner main jetting than what would be usual, normally requiring a further application of the accelerator. The beginning's of forcing engines to do that which they would not otherwise do without protesting... and then came mainstream injection, lol.
Would there be a noticeable difference between full enrichment at 5.5 or 6.0? Doubtfully.

[qikgts]

Interesting thought on the just-pre-fuelie-timing of these in this application.

It feels a little flat before the secondaries open at wot, which you can feel. I've still got 2.73's so it takes some time for it to wind up and I usually notice it if I drop from 5th to 4th at around 75 mph or so on the highway and mat it. If I go down to 3rd with a snap of the gas it's fine/less obvious. Most other conditions it's really good with no surging or bucking. Wanna say it has a .031 squirter with stock jets but IIRC I changed the pump cam.

This reared it's head (to the point it made me think about it anyway) once I changed out the stock exhaust. Feels like it leaned out some because it idles a little rougher now. Maybe a turn on all four corners would help?

[Walking-Tall]

Okay, well at WOT, all timing and operation of the power valve is irrelevant besides that it's wide open. Ever change the secondary spring? You might try a lighter/sooner spring if there's a flatness prior to them opening and no secondaries "kicking in" feeling. Yes, back into 3rd gear and you've got much more velocity happening, and would notice any flatness less.

Less restrictive exhaust could totally now be calling for more WOT fuel. But again, that's mostly the job of the secondaries, but trying a couple steps up in jet size in the primaries could perk things up in the areas of running prior to when the secondaries open.

A turn at all four corners? Idle mixture screws? If the idle's changed a bit, sure, re-adjust them (for smoothest idle/highest vacuum) by all means, and the idle speed if doing that changes it.

[qikgts]

When I get a chance to play with it some I'll be sure to have some bowl gaskets, jets and maybe a secondary spring kit in hand. I'll update at that point.

Thanks for the input.

[qikgts]

Anyone else have any input?

[JACook]

I'm not clear on the problem you're trying to solve, but Ford did a pretty darn good job matching the
main jets to the annular boosters in the 4180C, so I wouldn't go too wild there. What sounds tiny by
regular 4160 standards, really isn't.

The two stage power valve gives you a more progressive enrichment curve, rather than the two-step
deal you get with the single-stage valve. That helps light acceleration without having to kick in the full
enrichment as early.

If the problem you're solving is with the transition to the secondaries, I would start by making sure the
check ball is in the apply passage. Secondary bog is almost always a sign they are opening too early,
and/or too quickly. It can also be a sign the fuel level is too low in the secondary bowl. Properly tuned,
the secondaries should not announce their opening point at all. It should just be a seamless build of
power as the tach climbs.

Generally speaking, a less restrictive exhaust tends to improves booster signal to the carb, so if anything
you may be running a little bit rich, especially if you jetted up to compensate for oxygenated fuel. When
I installed my current Magnaflow X pipe on my '85 hatch, I ended up going back to the stock #62 jets
up front. (I also run JBA shorties.)

[qikgts]

Jeff thanks for the input. What Walker part number from the chart above looks to be comparable to the stock 2 stage valve?

[JACook]

It depends on the specifics of your engine, and how much manifold vacuum you have, but it would be
somewhere between the 70-25 and the 70-68.

It also depends on if you're trying to solve a light acceleration flat spot, or just looking for a bit more
fuel mileage. The power valve rating has no bearing on idle or heavy acceleration.

[RazorbackGT]

So does anyone know for sure what power valve comes with the Holley 3-1346 renew kit? It looks to me like a Walker 2 stage of some unknown size. Holley says it's a Holley 4.5 single stage. My car at idle is 20+" HG so I'm thinking I need a 9.5 and would probably like to go back with the 2 stage. As of right now, when I go to take off in first gear the car stumbles below 1600 RPM and if I punch it, it will die. Now if I rev up above say 1700 RPM or higher, it of course runs great. It's kind of annoying though when you just want to drive normally though.

[Walking-Tall]

RazorbackGT:
I'm not sure where you're still seeing a two-stage power valve shown within the 3-1346 kit, but here's what's at Holley's web site, showing 3-1346 with a single stage power valve:



As well, there's an addendum PDF file regarding PV's -----> http://documents.holley.com/199r10645.pdf

Idle manifold vacuum really is irrelevant for this subject, and really isn't a good way to specify a power valve. Going by 1/2 idle manifold vacuum is a really REALLY rough ballpark way of specifying for a power valve's vacuum level for opening. During cruise, moderate acceleration (acceleration enough that the main circuit is what's doing the fueling, otherwise the power valve contributes nothing to idle/off-idle) vacuum amount is more appropriate for putting the right power valve in. A 9.5 will work okay if a bit more than moderate acceleration drops the manifold vacuum below 10. If something is geared so or is on the low side on horsepower, lower number power valves become necessary so that additional fueling to the main jets isn't added when unnecessary.

Take off and such at low RPMs (like 1600-1700) has everything to do with the idle and off-idle circuits, and nothing to do with the main circuit or the main circuit's power valve, unless the power valve's diaphragm or gasket is leaking. Dying upon punching it points to inadequate or a malfunctioning accelerator pump shot. Accelerator pump transfer tube o-rings, for carburetors that use an accelerator pump transfer tube between the metering block and main body, are a known trouble spot for leakage into the power valve's vacuum chamber, which leads directly into the intake manifold, and for general malfunction of the accelerator pump if those o-rings aren't in good shape.


As for kits with genuine Holley parts/gaskets (as well as a Walker kit) still available with a two-stage power valve, this Ebay seller * lists two kits. There's base kits, and there's another for more $ that includes the de-choke diaphragm. As his descriptions indicate, be sure and specify your LIST number if ordering. I have bought a number of items from this seller. He seems to have everything down to screws/nuts/bolts/etc, and the pricing is very reasonable.

* Ebay seller's store, 4180 search results: http://www.ebay.com/sch/m.html?_odkw...=4180&_sacat=0

[RazorbackGT]

I wish now instead of putting the money in this carb I would have just bought a new one. It is so frustrating, I remember my 86 Gt was so smooth and quick, now the stumble and hesitation that I can't seem to remedy ( or my mechanic). At this point I'll probably just put the carb on the back burner and replace it when I overhaul the engine and add a top end performance kit. I like the car a lot, I don't want a race car, just a good driver with some tire spinning fun.

[Walking-Tall]

All kinds of new carburetors today present their own set of different and inefficient issues. The best solution is working with what you have, and the older, the better. Personally, if I had to deal with a 4180, I wouldn't. There's far too many dime-a-dozen List-1850 600cfm vacuum secondary carburetors out there, that with minimal tweaking, and no special parts'n'pieces or procedures to make function, would work great on a stock or stock-ish small block.