Holley 670 SA on a ZZ4 350HO won't idle down - Team Camaro Tech
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post #1 of 39 (permalink) Old May 30th, 13, 07:43 AM Thread Starter
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Holley 670 SA on a ZZ4 350HO won't idle down

I need help solving this problem. I have a Holley 670 Street Avenger on my ZZ4 355HP/350 with normal dual plane intake. I cannot get it to idle down below 900rpm - not that it can't, but it won't adjust lower. A 300 rpm drop into gear on the Turbo 350 is a bit much.

Details: It runs great throughout the throttle range. Idle screws are set for max vacuum at 18". Curb Idle screw all the way off the tang. Plain secondary spring. Transistion slots set to square on primary and secondary. Idle timing is 10 degrees btdc. Plugs look good. Float bowls set to bottom of inspection plugs. There is no additional vacuum can advance happening at idle. PCV works right. No binding in linkage. I sprayed carb cleaner around the base and I hear a slight change on the linkage side.

Anybody had this problem? Help.
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post #2 of 39 (permalink) Old May 30th, 13, 08:34 AM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

Thoughts that come to mind... Choke lever binding up. If we're talking first gen here, the throttle lever may be binding up. Make sure the choke is fully open and not on the fast idle cam, then disconnect the throttle linkage and see if you can get it to idle down.

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post #3 of 39 (permalink) Old May 30th, 13, 08:59 AM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

Quote:
Originally Posted by TomcatSTL View Post
I need help solving this problem. I have a Holley 670 Street Avenger on my ZZ4 355HP/350 with normal dual plane intake. I cannot get it to idle down below 900rpm - not that it can't, but it won't adjust lower. A 300 rpm drop into gear on the Turbo 350 is a bit much.

Details: It runs great throughout the throttle range. Idle screws are set for max vacuum at 18". Curb Idle screw all the way off the tang. Plain secondary spring. Transistion slots set to square on primary and secondary. Idle timing is 10 degrees btdc. Plugs look good. Float bowls set to bottom of inspection plugs. There is no additional vacuum can advance happening at idle. PCV works right. No binding in linkage. I sprayed carb cleaner around the base and I hear a slight change on the linkage side.

Anybody had this problem? Help.
Your problem is clearly stated "Transition slots set to square on primary and secondary." The secondary needs to be closed down, that carb isn't designed to idle off the secondary, by doing so it is overriding the primary idle circuit! Close the secondary throttle blades completely so the screw is off the tang then tighten the screw until it makes contact with the tang then maybe another 1/8 turn so the throttle blades can't bind in the bores when closed.

...Dennis

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post #4 of 39 (permalink) Old May 30th, 13, 09:28 AM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by DjD View Post
Your problem is clearly stated "Transition slots set to square on primary and secondary." The secondary needs to be closed down, that carb isn't designed to idle off the secondary, by doing so it is overriding the primary idle circuit! Close the secondary throttle blades completely so the screw is off the tang then tighten the screw until it makes contact with the tang then maybe another 1/8 turn so the throttle blades can't bind in the bores when closed.
I hear you & thanks. I have struggled with this point because as Holley says it is a four-corner idle even though it only has mixture screws on the primary side. I see where some have said the transfer slot is uncovered on the secondaries and vice-versa, also. I can back the secondary screw out and the idle does not change for me.
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post #5 of 39 (permalink) Old May 30th, 13, 09:29 AM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by dnult View Post
Thoughts that come to mind... Choke lever binding up. If we're talking first gen here, the throttle lever may be binding up. Make sure the choke is fully open and not on the fast idle cam, then disconnect the throttle linkage and see if you can get it to idle down.
I can feel the weighted choke cam bouncing around freely after it warms up. Does this mean it cannot be on the fast-idle screw?
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post #6 of 39 (permalink) Old May 30th, 13, 10:21 AM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by TomcatSTL View Post
I hear you & thanks. I have struggled with this point because as Holley says it is a four-corner idle even though it only has mixture screws on the primary side. I see where some have said the transfer slot is uncovered on the secondaries and vice-versa, also. I can back the secondary screw out and the idle does not change for me.
I've had several 670 street avengers and never seen anything even suggesting 4 corner idle. Unless there are idle mixture screws on the secondary side it's not 4 corner idle!

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post #7 of 39 (permalink) Old May 30th, 13, 10:36 AM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

If the cam is free to move, yes, it is not on the fast idle setting/screw.
Eighteen inches of vacuum is excellent.
If place your hand(s) over the carb air horn, the engine should stop.
I would try the secondary side first because as suggested, the secondaries appear to be open slightly.
You can place some Scrotch® tape over the secondary transition slots ensuring it doesn't leak from them, including PCV.
Have you plugged each and every vacuum hose/port from the intake and carb?
Tighten the intake bolts?
You mentioned normal dual plane manifold. Holley is square bore, unless you have a Model 4360, 4165, or 4175 Spread-bore carb, matching a spreadbore manifold, but with 18" of vacuum, it seems to be covered.

As a last resort, change to a known carb and/or, turn down the mixture screws to the rpm desired.
Are you certain the carb does not have reverse-mixture metering plates? Very popular with emission carbs of the '70's and not saying a plate may have made it into the production mix, but you have to eliminate the variable.

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post #8 of 39 (permalink) Old May 30th, 13, 11:07 AM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by DjD View Post
I've had several 670 street avengers and never seen anything even suggesting 4 corner idle. Unless there are idle mixture screws on the secondary side it's not 4 corner idle!
http://www.holley.com/0-83670.asp

It is listed that way under "Features" on the Holley web page. Is it a four-corner with no adjustment on half, then?

I expected the idle to drop when I backed the screw out, but it did not. So, I put it back where I had it.

Come to think of it, I adjusted the Primary slot to square and then adjusted the secondary butterflies to look exactly the same with a light shining through.
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post #9 of 39 (permalink) Old May 30th, 13, 11:14 AM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by Everett#2390 View Post
If the cam is free to move, yes, it is not on the fast idle setting/screw.
Eighteen inches of vacuum is excellent.
If place your hand(s) over the carb air horn, the engine should stop.
I would try the secondary side first because as suggested, the secondaries appear to be open slightly.
You can place some Scrotch® tape over the secondary transition slots ensuring it doesn't leak from them, including PCV.
Have you plugged each and every vacuum hose/port from the intake and carb?
Tighten the intake bolts?
You mentioned normal dual plane manifold. Holley is square bore, unless you have a Model 4360, 4165, or 4175 Spread-bore carb, matching a spreadbore manifold, but with 18" of vacuum, it seems to be covered.

As a last resort, change to a known carb and/or, turn down the mixture screws to the rpm desired.
Are you certain the carb does not have reverse-mixture metering plates? Very popular with emission carbs of the '70's and not saying a plate may have made it into the production mix, but you have to eliminate the variable.
The intake sure seems untouched from GM as it is a crate motor. I know the car will stall if I cover up the secondary horn. The needles seem to act as I would expect and either will stall the motor if shut - they are both 1/2 turn from closed for mixture. I did not think of plugging the brake booster! I will try that when I get home tonite. Thanks
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post #10 of 39 (permalink) Old May 30th, 13, 11:23 AM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

Quote:
Originally Posted by TomcatSTL View Post
http://www.holley.com/0-83670.asp

It is listed that way under "Features" on the Holley web page. Is it a four-corner with no adjustment on half, then?

I expected the idle to drop when I backed the screw out, but it did not. So, I put it back where I had it.

Come to think of it, I adjusted the Primary slot to square and then adjusted the secondary butterflies to look exactly the same with a light shining through.
Okay something new to me, I dug a bit and found they now make what is called an "Ultra Street Avenger" which has 4 corner idle and 4 mixtures screws.

Unless you have an "Ultra" with 4 mixture screws, close the secondary throttle blades down and be done with this problem...

...Dennis

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post #11 of 39 (permalink) Old May 30th, 13, 11:28 AM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

Quote:
Originally Posted by DjD View Post
Okay something new to me, I dug a bit and found they now make what is called an "Ultra Street Avenger" which has 4 corner idle and 4 mixtures screws.

Unless you have an "Ultra" with 4 mixture screws, close the secondary throttle blades down and be done with this problem...
I am ready, Man!

Backing out the secondary stop screw didn't drop the idle, though. I wonder if I have a jacked-up base plate?
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post #12 of 39 (permalink) Old May 30th, 13, 12:16 PM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by TomcatSTL View Post
I am ready, Man!

Backing out the secondary stop screw didn't drop the idle, though. I wonder if I have a jacked-up base plate?
Did the secondary throttle blades close?

It should give control back to the primary side allowing you to control the idle with the primary throttle adjustment screw and idle mixture screws. At this point I would be inclined to set the carb back to out of box spec's and start fresh.

...Dennis

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post #13 of 39 (permalink) Old May 30th, 13, 01:53 PM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by DjD View Post
Did the secondary throttle blades close?

It should give control back to the primary side allowing you to control the idle with the primary throttle adjustment screw and idle mixture screws. At this point I would be inclined to set the carb back to out of box spec's and start fresh.
You are right - it should. I have been around the block with this particular carb enough. I ordered the updated genuine 4-corner version.

Thanks for your help.
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post #14 of 39 (permalink) Old May 30th, 13, 07:49 PM
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

If the mixture screws are only out 1/2 a turn, you need to go up on the outer idle air bleeds, ideal is 1 1/2-2 turns. Does that carb have replaceable bleeds?or you needs to put
020 wire in the idle feed restrictors, you need to lean out the idle circuit, either more air or less gas. Agree on the secondary throttle plates.

If you turn out the idle mixture screws, does it lower your idle?

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post #15 of 39 (permalink) Old May 30th, 13, 08:19 PM Thread Starter
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Re: Holley 670 SA on a ZZ4 350HO won't idle down

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Originally Posted by 1971ls6 View Post
If the mixture screws are only out 1/2 a turn, you need to go up on the outer idle air bleeds, ideal is 1 1/2-2 turns. Does that carb have replaceable bleeds?or you needs to put
020 wire in the idle feed restrictors, you need to lean out the idle circuit, either more air or less gas. Agree on the secondary throttle plates.

If you turn out the idle mixture screws, does it lower your idle?
This sounds like very good advice. I believe your plan would work. It is a clean, recently rebuilt carb so I am going to let it go on eBay for a fair price rather than drill or plug it. Really, the only fault I have with it is this last 100rpm at idle!

So, I have a 4-corner All-Aluminum 670SA coming fedex tomorrow - I think it is likely the added adjustability on the idle should allow me to square it away.

Cheers

Last edited by TomcatSTL; May 31st, 13 at 09:28 PM.
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