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Old 11-05-2006, 05:24 PM   #1
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Edelbrock Gurus, Edelbrock Idle circuit help

I've got an edelbrock 7011 and I've got a lean spot just off idle. If I adjust the carb for best lean idle as in edlebrocks tuning manual, the problem is really bad but it gets much better if I turn the idle mixture screws out about 3 more turns. (the transfer slots are tied to the idle mixture circuit) My problem is that this is only getting me so far and i think I've maxed out the fuel that I can get by turning out the idle mixture screws.

It idles at 7-8" of vacuum so thats really the root of the problem. since the idle circuit works on pressure differential, less vacuum = less fuel. I know my motor is a bit more radical than suggested for this carb but I was hoping I could make it work. Suggestions?

I've read about a modification for this on holley carbs here: Living With A Carburetor…Every Day Can this modification be done on the edelbrock carb?

My combo; 355 with an RPM air gap intake, Edelbrock #7011 carb (750 cfm)AFR 195's, 9.5:1 cr, Lunatti Hyd roller 231/239 @.050 .535/.550 lift, 110 LSA. I've got a 9" rear with a 3.50 gear and a T56 with (as I recall) a 2.66 first gear.
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Old 11-05-2006, 05:59 PM   #2
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before you start drilling this and that. recurve the distributor for as much initial advance at idle as your starter motor will tolerate. Were talking 20-24deg at idle. More is better. You have to limit the mechanical advance travel in the distributor, not just swap springs to get this effect. This will increase manifold vaccum and idle speed allowing you to close the throttle blades down more at idle. This will clean up the idle and should help your off idle lean spot a lot. The throttles must be in the "sweet spot" relative to the idle transfer slot at idle or the idle circuit gets all messed up. Be sure to employ a working PCV and vented valve cover. This PCV adds to the available airflow at idle. Make sure you do not have a manifold vacuum leak or you'll have to richen up the idle to compensate for the lean cylinder (air leak). resulting in a even worse off idle flat spot.

I've run my Edelbrock on motors with much much more radical cams and intakes without haveing to resort to drilling throttle blades. You can too.
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Old 11-05-2006, 06:54 PM   #3
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Yep, my base advance is 20 degrees(distributor has 16 mechanical)... starter still turns it over but as you would expect it has a hard time.

I am running a pcv with breather.

The amount of required throttle opening for idle is minimal so I'm not suffering from the problem where the transfer slot is under the throttle blades.

I've always understood that you want to be at the bottom of the transfer slot... you use the word "sweet spot" though so I wonder if you are trying to say something else.

This is the part of the article I linked that I'm refering to and the same problem I beleive I'm having: Patterson follows up with a lesser-known procedure--checking the off-idle circuit. This is what "bridges the gap" between the idle and main fuel circuits for a smooth power transition, also known as tip-in. Crank up the idle speed screw and verify that the engine rpm increases proportionally. When you see fuel dribbling from the boosters, back the idle speed down until they stop dripping fuel, and you're smack-dab into the off-idle circuit. Turning the mixture screws clockwise or leaning the mixture should reduce engine rpm, and richening the screws should increase rpm. Our engine rpm didn't increase when we tried richening the mixture because our idle-feed restrictions were drilled too small. Enlarging them, in our opinion, is carb guru territory.

Sidebar on the article: Patterson drilled our idle-feed restrictions 0.003-inch larger to help richen the off-idle circuit. (there is an accompanying photo)
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Old 11-05-2006, 11:08 PM   #4
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Your carb is a leaner version of mine (Edelbrock 1407)
Do you know the drill size of the idle feed restriction and idle air bleed? mine is plenty rich at idle and off idle.

What happends when you position your carbs throttles as described in the article and then add a little fuel manually by dripping a bit down in the carb while its running at this high idle point? Or just choke off some airflow with your hand.
Does the motor pickup rpm briefly before dropping off from retricted airflow?

I still think you have a vacuum leak. Do a cylinder balance test. Find what cylinder drops the least rpm when it is disabled (spark) temerairly when the throttle is open to the troublesome off idle point.
You want to eliminate all possible faults before ya start drilling cause its hard to reverse those mods. Can cause you to loose your whole tune if you mess with the basic idle circuit tuneup to cover up a simple vacuum leak fault.

Last edited by F-BIRD'88; 11-05-2006 at 11:12 PM.
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Old 11-08-2006, 07:38 PM   #5
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Well, you've definatly got me thinking your way about this. I've been in contact with Edelbrock and Lunatti... Edelbrock says all their carbs use the same idle circuit jetting so since we know that you and other guys have run cams bigger than this on other edelbrock carbs, this isnt a problem with this model of carb with too big a cam.

Lunatti seems to think that the cam should make around 13" of vacuum so you guys have talked me into the conceeding that I've got a vacuum leak.

I've done the thing where you spray carb cleaner around looking for a change in idle speed and didnt find anything. So I remember haveing issues once with some hyd. lifters so I checked that out. Even though mine were only preloaded 1/4 turn, by backing them off just to the point of zero lash and a hair more i've picked up 1-2" of vacuum so I'm at 9-10" now... This is with 20 degrees initial advance + 15 mechanical and around 40 degrees at 1000 rpm idle with the vacuum advanced hooked up to manifold vacuum.

So I guess now I'm looking inside the motor to see if maybe a valve is not sealing or if I've got a gasket leak on the bottom of the intake where it seals against the head. What do you think?


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Originally Posted by F-BIRD'88 View Post
Your carb is a leaner version of mine (Edelbrock 1407)
Do you know the drill size of the idle feed restriction and idle air bleed? mine is plenty rich at idle and off idle.

What happends when you position your carbs throttles as described in the article and then add a little fuel manually by dripping a bit down in the carb while its running at this high idle point? Or just choke off some airflow with your hand.
Does the motor pickup rpm briefly before dropping off from retricted airflow?

I still think you have a vacuum leak. Do a cylinder balance test. Find what cylinder drops the least rpm when it is disabled (spark) temerairly when the throttle is open to the troublesome off idle point.
You want to eliminate all possible faults before ya start drilling cause its hard to reverse those mods. Can cause you to loose your whole tune if you mess with the basic idle circuit tuneup to cover up a simple vacuum leak fault.
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Old 11-08-2006, 08:14 PM   #6
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what happens if you use your hand, a rag or the choke flap to "choke off" some airflow to enrichen the mixture? does the idle pick up?
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Old 11-08-2006, 08:14 PM
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