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Old 04-07-2013, 06:19 PM
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You can start by closing (backing out) the fast idle screw, which will close the throttle plates, until the exposed transfer slot on the venturi wall is a square. The more that's exposed, the more fuel it's pulling over. Start with the idle mixture screws out about 3/4 of a turn, and work them at the same time to get the highest idle with the least throttle opening (fast idle screw).

There are adjustments in the metering rods and spring changes for long duration cams, I doubt that's a problem with your setup. I have one 1405 and one 1406 on a tunnel rammed big block with a 292/302 cam and haven't had to mess with them. It did take some finess to get them adjusted correctly, but not a big deal.

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Old 04-07-2013, 07:08 PM
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Quote:
Originally Posted by 68NovaSS View Post
You can start by closing (backing out) the fast idle screw, which will close the throttle plates, until the exposed transfer slot on the venturi wall is a square. The more that's exposed, the more fuel it's pulling over. Start with the idle mixture screws out about 3/4 of a turn, and work them at the same time to get the highest idle with the least throttle opening (fast idle screw).

There are adjustments in the metering rods and spring changes for long duration cams, I doubt that's a problem with your setup. I have one 1405 and one 1406 on a tunnel rammed big block with a 292/302 cam and haven't had to mess with them. It did take some finess to get them adjusted correctly, but not a big deal.
Doh! I've been starting with the idle screws out 2 full turns.

The builders said I needed a 700-800cfm carb. I just hadn't gotten one yet.

Adventures in auto repair: I was checking the torque on my intake, 25lbs on each bolt, got to one of the little ones when I heard a loud and dreaded POW!

My reaction was like this: Instant No Button! Star Wars funnies FTW!

So I just got done after pulling my intake off, getting the stud out (thank God it wasn't stuck in the block), driving out to one of the stores for new intake gaskets and Lowe's for good quality bolts, and slapping it back on. Now I have to wait 'til tomorrow after work for the RTV to cure.

Moral of the story, Edelbrock intake bolts suck, and you can only use them once.

ETA: did you mean for me to loosen out the idle speed screw or the fast idle screw to close the throttle plates?

Last edited by SoCalExile; 04-07-2013 at 07:33 PM.
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Old 04-07-2013, 11:20 PM
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Isn't that the same adjustment, that opens the throttle (and plates) when turned inwards. Make sure the adjustment screw is on the low step of the fast idle cam.
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Old 04-08-2013, 07:19 PM
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Ok, so the idle screws are backed out 1 3/8 out. with the park idle set to about 1000-1100.

What Ive noticed is that in drive at a stop, the rpms will be round 750-850 then it'll dive down to 550 and want to die.

When I pull the manual choke and close the butterfly a bit, the rpms even out and stay rock solid.
What am I doing wrong?
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Old 04-09-2013, 10:53 AM
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Yeah after talking to others the rpm drop is likely caused by too low of a stall.

The cam is rated 1800-5800. I was told the stall should be 200-400rpm above the minimum of the cam = 2000-2200.

The stock stall of the c6 is likely around 1800 give or take.
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Old 04-09-2013, 04:22 PM
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It sounds like you are headed in the right direction.

The idle mixture screws do not need to be synchronized. For instance back them out one turn from fully seated. Then continue backing each screw out some until your run on is cured. Then set the idle for rpm. You could also check the stall speed on your vehicle. The higher the stall speed the faster it will come off the line.
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Old 04-13-2013, 05:55 PM
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Update for those searching for answers to the same issue.

The 300rpm drop from park to drive is no doubt the torque converter. The instability with the idle once in drive is due to an issue with Edelbrock carbs where they don't like fuel pressure above the 4.5-5.5 psi range.

Today I rebuilt and cleaned the carb with no luck. The idle screws weren't doing a damn thing and it wasn't idling like a well-adjusted machine. So I played a hunch after reading about the fuel pressure issue and bought a cheapie Spectre fuel pressure regulator, slapped it on and set it to 4.5 psi. Problem solved! It now stays a steady idle and I can actually tune the carb with a vacuum gauge now.

Next month I'll spring for a decent regulator.
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