Holley Power Valve Question

[Michael Hampson]

It's been quite a while since I posted last, but I've got a question for you Holley experts out there.

I replaced the carburetor on my stock '64 365HP 327 with an original style (but wrongly dated) Holley '2818-1' 4150 (600CFM). I rebuilt it with a non-Holley kit (which I shouldn't have I know...) and everything is fine with it EXCEPT that I get a brief power lag when I step on the gas. Accellerating normally from a stop it's fine, but step on the gas with any authority at all and I get the lag.

I assume that the power valve that I got with the general kit is not a low enough number to handle the low manifold vacuum on this SHP engine. Does this statement make sense or is it real obvious I am no expert?

If I'm making sense, what Holley power valve is recommended for this application? Any special recommendations? I'd prefer not to have to do this by trial and error. I think the 2818 last carb I had (borrowed from a friend) had a 65 (6.5" H2O).

Thanks for your help!

Michael

[Wayne K.]

Re: Holley Power Valve Question

Have you tried to make any adjustments to the accelerator pump setting ?

[Joe C.]

Re: Holley Power Valve Question

Michael:

I, too used a non Holley kit for the 2818 feeding my 327/365. I then bought a Holley power valve #65 and installed it, keeping the valve supplied in the kit as a spare. I agree that you should also check your accel. pump setting.

A good source of tech. info can be found at www.holley.com.

Joe

[John H.]

Re: Holley Power Valve Question

Michael -

Most Holley "sags" can be cured with adjustments to the accelerator pump linkage or re-positioning the accelerator pump cam; sometimes it also requires changing the pump "shooter" size. The power valve is seldom the culprit for this symptom.

[george romano]

Re: Holley Power Valve Question

Having had many Holley carbs over the years, on various size engines, it sounds more like the secondary throttle blades are opening up too early. I suggest replacing the secondary diaphram spring with a heavier one, as this will delay the secondary's opening long enough to eliminate the bog. I don't think the power valve is your problem. The number on the power valve dictates when it should open, and enrich the fuel mixture. That number should be higher than your idle vacuum reading. I cannot remember the exact formula to figure out which power valve you need, but I remember it being 10 (lbs, inches?) above idle vacuum.

George

[Michael Hampson]

Re: Holley Power Valve Question

Thanks, guys,

I will first look at the accellerator pump cam and pump adjustment before I remove a bowl and play with the power valve.

Thanks for your help!

Michael Hampson

[Jim T.]

Re: Holley Power Valve Question

George you are going the wrong way on your power valve. A 65 Holley power valve opens at 6.5 inches of vacuum. I would have to locate my information to be sure, but I believe the recommended power valve is one that is at least 2 inches below what the engine vacuum is at when at idle.
In my 68 327/350 HP running a non-original carb I use a Holley with a 6.5 power valve. In my 70 with a ZZ1 350/345 HP crate engine which has less vacuum at idle, I use a 45 power valve which opens at 4.5 inches of vacuum.