Power valve question???

[z ya]

I have never been able to get the idle right in

my 3310 holley. Could a blown power valve affect the idle?

[blueovalz]

To answer that question, we need some more info. What is wrong with the idle? Too rich? Lean? Unstable? What kind of cam, transmission (in gear or out of gear), and idle speed do you have? Do you have a good vacuum signal? Are the plates nearly closed, or are they adjusted to a partially open open position just to get it to idle? Sorry for all the questions, but the answer needs this.

[fl327]

a blown power valve makes the idle ultra rich, and you can hear vaccum noise in the primary at idle if its really messed up.

[z ya]

Cam is 236 at 050 with 490 lift. The idle is erratic both in gear and in park. I also have

a 2000 rpm converter is way to tight from what

I have been told. Should have between 2800 to

3000 stall. I tried drilling the throttle blades

with 1/16" holes but this didnt seem to help much.

When the car is idleing in park it will slowly

start to creep down in rpm's. Idle speed is set

at about 750 in park. When I put it in drive it

lugs down bad and wants to die.

[John Scott]

For a performance engine, long duration ect, check your vacuum in neutral if standard trans, in drive if auto. Use a power valve about 2#s lower than vacuum reading. Example if you have a reading of 8.5", go to a #6.5 power valve. For more of a stock engine the vacuum reading will be taken at a steady cruise speed.

John

[Guest Anonymous]

"Cam is 236 at 050 with 490 lift. The idle is erratic both in gear and in park."

 

I think this is your idle issue. Cams that big just don't want to idle, at least not down at 750 rpms or lower. They have little vacuum signal so the idle circuit is screwed up from the get-go. Just an opinion, but IMHO its a tradeoff for a larger performance cam, idle quality/drivablity VS Performance, you can't cheaply have them both IMHO.

 

That said, follow John's suggestion for matching the powervalve to the correct vacuum. Its low vacuum could likely be causing the powervalve to dump in fuel because it thinks it sees a load condition on the engine.

 

One more thing, the Holley blown powervalve problem that persisted, is pretty much fixed these days, most newer Holley carbs will already have the blowout proof powervalve check valve installed.

 

Regards,

 

Lone

[z ya]

Thanks guys , I will give it a shot.

[pparaska]

Spectre and Holley both make a cheap kit with a one-way valve and drill bit to put power valve protection in the older Holley's - I installed one the other night in my 600 vac sec carb.

 

You can check the power valve by sucking (after all the fuel is dried off!) on the large side of the valve and seeing if air leaks through. There's a tester adapter also, but I don't think it's necessary.

 

I have a cam with the same kind of specs (236/240 @ .050, .501/.510 lift, solid flat tappet Comp Xtreme PN 12-677-4) in my 327 and it's pretty lopey at idle. With that kind of cam timing, and 10:1 compression, it's difficult to get idle below 1000 rpm with an auto in gear. It's the price you pay for having a lopey cam that'll make the engine breathe above 6000 rpm. I'm going down to a 600 cfm carb from a 750 to try to get better idle and transition performance -af ter much brow beating by Jamie and Mikelly . I may try the 600 body with the 750 throttle plate after grinding a transition in the body. I've heard this is a good way to bring the venturi signal up on a carb, and it gives about 650 cfm of flow. This is the same setup a 650 DP (4777) uses.