I just bought a spring kit from E-Br and it came with not one sheet of info on the vaccum ratings of the springs. I want a spring 2 inches below idle in drive, but I have no idea what the springs are rated at.

I see orange red blue purple yellow, and thats about it....

What vaccum ratings do these come in at?

Gold = 4"
Orange = 5"
Black = 6"
Yellow = 8"

So yellow is the one that opens the Fastest???

I was told to get one thats 2 inches below my idle in drive vaccum, which is about 15inches
.

WIll the yellow work?? Thanks

Monte,

when the power valve pops up it enriches the main circuit. Unless your car is idling on the main circuit (the fuel is coming out of the booster venturiis) the power valve is irrelevent to the idle quality or vacuum. This is an old magazine deal that has somehow become embedded in the hot rod culture. run the stiffest spring, it'll open the power valve faster when when you get on it while driving down the road.

Tom

It may be irrelevant to idle quality, but it sure will effect the part throttle mixture as you're running down the road.
The yellow being the stiffest will lift the rods the earliest, and cause the mixture to go to rich when you're cruising around town. Not always what you want.
If you can run a vacuum gauge into the car where you can see it, it will tell you alot about where it is coming online.

I disagree with the power piston not affecting idle. The rods should be seated but there not the same size as the jets I think. I have heard this multiply time.The idle metering circuit on a Q-Jet is not an independent, stand-alone circuit. The idle mixture screws in the throttle plate receive their fuel through the main metering jets. Thus, a change in the main metering circuit (jets and/or rods) will affect the idle circuit. The idle mixture screws cannot meter more fuel than the main jets/rods will allow.

The springs a many different lengths. The taller ones are alot sponger than the short ones. I just want the power piston to seat at idle, because right now its not. I have a pen spring in the power piston springs place, and yes it does work....

Either way, if your engine idles at 15", you'll want the stiff 10" in there for sure. If you want to test it, hook up a vaccum gauge and see exactly where you'd want some mid throttle 'punch' to come in. Bet its at 9-10".

A pen spring, huh :D ? What kind of carb is it? A qjet?

Anyway, Yea, I have that kit too... Edelbrock has the list on their site, I think. They werent painted all that well though. I too was wondering just exactly the point of that short spring. Lars Grimsrud has a way of checking the stiffness of the springs with washers and a nail, its on corvetteforum.com.

I wonder why nearly ALL Holleys come with 6.5 or 8.5 PVs (and they seem to be OK), when it seems like most cars would need a 10 or so. Just curious.

Ok, I have that part down, I want a spring that comes on at around 8-10.

Now how are these things rated? Is it like a power valve? 8hg means it starts letting the metering rods lift out of the jets at 8hg? This might be bad since the rods theoritical would not be out of the jets at cruise because I have more than 8 inches of vaccum, or at least I think I do....

So is the rating for a the stiffer but shorter spring pop the rods out faster, yet, it has a lower HG number. Im so confused right now that its unbelievable.

Are the taller springs, which are loosely coiled, allow the power piston to come up faster and smoother than the short tightly coiled springs.

Is the HG messurement how much vaccum it takes to suck them down. I need a spring that will seat with about 15inches of vaccum.

The power piston is under suction from engine vacuum. Your highest vacuum is at idle, or deceleration. As you open the throttle the vacuum drops and the spring under the piston is able to overcome the suction and lifts the rods out of the main jets, increasing the jet area, and richening the mixture. So the stronger the spring the earlier it pushes the rods out of the jets. In other words the spring rated at 8" will richen the mixture the earliest. The longer the spring the more force it stores when compressed.

A power valve on a holley, is just that. A valve. It does not enrichen the mixture, only provides a greater volume of fuel to the jets. Therefor you cannot compare the two systems, because one is for enrichment, the other is for volume.

Monte,

Yes, I know you've seen it multiple times. It's still wrong. If you have a 72 jet with a 48 rod, there's room around the rod in the jet. The fuel that goes between rod and the jet is what your car runs on when you're idling or driving down the road at steady speed. When you accelerate or hit a steep hill you open the throttle and the vacuum drops. Then the power valve pops up, and the small diameter tip of the rod is in the jet and much more fuel is availble. However, the amount available when the rods are down is enough to run your car at 70-80 MPH steady state. This is somewhere between dozens and hundreds of times more that it needs at idle. That's why it's irrelevent whether the rods are up or down at idle.

The rods do not ever "seat" in the jets. The downward travel of the power piston is stopped by an adjustable device in the piston well. The thick part of the tapered section of the rod below the step is in the jet then, same as when you're driving down the road at steady speed.

If you have a pen spring in there it will hold the piston and rods up all the time, your engine will run at full rich all the time. Buy stock in companies that make spark plugs, you'll be buying them by the case. smile.gif A pen spring is not close to a power valve spring at all.

Incidentally, you do not want the power piston up when driving normally. It called the power enrichment system for a reason.

Buzzbomb, most all of the Holley carbs sold new on performance Chevys had a 105PV in them. This does not include the small squarebowl Holleys installed on some 327's, it had an 85.

Truth is it usually doesn't make much difference, when your typical Chevelle owner slams his foot to the floor the PV is going to be up or open by the time pedal hits carpet anyway.

I use the GM part # 7037305 PV spring, it's equivilent to somewhere between an 85 and 105 Holley PV number, was OEM on early '70s 350 Corvettes.

Tom

TJC,

IMHO, that stuff you just posted about the PV in a Holley is wrong. Under low vacuum conditions the PV supplies fuel to two precision-drilled passages that essentially bypass the main jets and dump fuel directly into the main wells. Both systems work about the same, they supply a richer mixture under power conditions. The exact size of that drilled hole corresponds to the difference in size of the power tip and lean cruise parts of the Q-jet metering rods.

Clear as mud? Good. smile.gif

Tom

Originally posted by Tom Mobley:
Under low vacuum conditions the PV supplies fuel to two precision-drilled passages that essentially bypass the main jets and dump fuel directly into the main wells. Both systems work about the same, they supply a richer mixture under power conditions. The exact size of that drilled hole corresponds to the difference in size of the power tip and lean cruise parts of the Q-jet metering rods.

*Not so creative edit :D

Buzzbomb, most all of the Holley carbs sold new on performance Chevys had a 105PV in them. This does not include the small squarebowl Holleys installed on some 327's, it had an 85.

Truth is it usually doesn't make much difference, when your typical Chevelle owner slams his foot to the floor the PV is going to be up or open by the time pedal hits carpet anyway.

I use the GM part # 7037305 PV spring, it's equivilent to somewhere between an 85 and 105 Holley PV number, was OEM on early '70s 350 Corvettes.
Tom,

Thanks for clearing that up about the Power Valve opening rates. I suppose if 10.5 came on HiPo Chevys stock, that that rate would be best for really anything comparable.

I too wondered about the statement of Holley and Qjet, AFB being totally different. I have always known Holleys like you said- under low vacuum, the power valve switches open and enriches the mixture via its own metered passages, not the main jets. In theory, if it was just to increase fuel volume through the jets, how could it do it when the jets are the same size as they were to begin with? IN other words, how could you increase volume from an orifice that didnt change in size, only had more fluid to pass? Afterall, Holleys dont have metering rods. Seems to me if that was the case, the power valve would actually be a restriction. IF it theoretically DID pass its fuel THROUGH the jets, whats teh point of the power valve at all? Why not just use bigger jets. I know this is not the case, just wondering out loud.

Thanks for posting the part number for that spring. I might see if the dealer has it (which I doubt- but?).

Buzzbomb,

A holley power valve is good for around 8-10 jet sizes. You can yank the PV, install a plug and increase the jets 10 sizes or so, some do this for drag racing. Problem is it'll be so pig-rich just driving around that the spark plugs will need to be changed constantly. There would also be a severe wallet hit at the gas station. At WOT it would be the same as it was. Just guessing, what percentage of the time you're driving your car do you have the gas padal floored?

the deal is that mixture requirements for cruise and WOT are different, a lot different. one won't work in place of the other. That's why carbs have power circuits, and they need to work right.

Tom

Thanks Tom. I should know better than to regurgitate facts from other sources. You are correct.

I got everything back together, with the yellow spring. It runs unbelieveable, but....

Theres always a but right???

The thing will not start when it is hot off the highway. If you drive it anywhere else but the highway and shut it off it will start. Its like the damn thing has vapor lock or something. After 30 secs of trying to start it, it smokes black. Some how it is flooding itself when it sits.

I think it might be the coil too, because it is 1973 issue. This car is all origanal, even down to the 1973 coil. Its weird that way. Only has 200,000 miles too, hmmmm. Think the coil might be a bit weak..

Other than that im happy, the throttle response is nice, has good part throttle response, everything seems to work well, except the hot start. Any ideas??

Thanks

Try this to test the coil; turn the ignition to on for 3 full seconds, and then turn to start.

Also, you must run a heat barrier of some type with a QJet.

For future reference, the average stock Qj has the ~8"h.g. spring in it from the factory.

Mike