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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 09-14-2000, 10:32 AM   #1
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idle mix adjustment on Edelbrock carb

I've got an Edelbrock 600cfm carb on the 350 in my Camaro. The engine has a cam with specs of 0.488" lift, 292 adv. dur./234 0.050" dur. The intake is a Holley dual plane street dominator. My problem is that I can't get any adjustment on the idle mixture screws. The idle is set at 800 rpm, and I've got the lighter (yellow) springs in the carb. The car is running rich, and nothing I do leans it out! Please help!
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Old 09-14-2000, 11:29 AM   #2
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Are you sure you do not have a vacuum leak? What kind of vacuum reading are you getting? Is the timing set right?

Is the carb new or rebuilt?

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Old 09-15-2000, 08:50 AM   #3
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You can't do much to lean out overall operation without a calibaration kit. You can lean out the idle with the idle adjustment screws but I'm assuming you don't mean a rich idle...

Doesn't seem like that carb should be rich out-of-the box for your setup, though. If you are running too much fuel pressure, you could be blowing by your needle seats causing a terribly rich condition.

What is your FP and/or fuel delivery setup???

[This message has been edited by FastBroker (edited September 15, 2000).]
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Old 09-16-2000, 04:58 AM   #4
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fast broker is right, have you tried some jet/metering rod changes as per the edelbrock tuning guide? If its just rich at idle the only real adjustment would be through the idle screws or some air bleed wizardry that i dont know about
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Old 09-17-2000, 01:18 AM   #5
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ok i did a little refreshing of my AFB knowledge and i think i might know what your problem is, this from the edelbrock tuning guide at www.edelbrock.com about the idle circuit

"...and the highly aerated mixture then
moves through the passages in the main-body to the location of the Transfer Slot (7) and Idle Screw Port
(8). The Transfer Slot (7) is a large air bleed when the throttle is closed, but as the throttle is opened the
slot is exposed to manifold vacuum and becomes a discharge port for Idle System fuel. The Idle Screw Port
is a variable discharge restriction that is adjusted by the engine tuner to achieve the desired A/F Ratio at
engine idle. "

if you look in your carb in the primary barrels youll see on the front side of the barrel two small holes, the one on the bottom is the idle screw port where the fuel at idle SHOULD only come out, but for example, on your motor, youve increased the idling rpm which theoretically will start drawing fuel out of the transfer slot which is the slot hole above the small pin sized hole in the barrel.

I would think the solution would be to drill two very small holes in the primary throttle blades so you dont have to have the throttle open so much. Ive seen holleys that had this done for similar reasons. Im no carter expert so if i were you id pick up a carter book (i think dave vizzard wrote one??) and im sure they would have this info in there

im assuming you are just running a rich idle
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Old 09-17-2000, 01:23 AM   #6
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BTW thats if all else fails, like you have the idle mix screws all the way in
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Old 09-19-2000, 04:02 AM   #7
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OK, the carb is rebuilt. I thought that maybe the cam was keeping the vaccuum too low at idle. What sort of vaccuum reading should I have? How should I check for vaccuum leaks? I checked around the base of the carburetor by spraying starting fluid. I figured if there was a leak there, sprayed fluid would get drawn into the manifold and make the engine rev a little higher. That didn't happen, so I don't think there's a leak there. I have an electric fuel pump, and a pressure regulator that is presently set at 6 1/2 psi. I'll try turning it down and see if that helps.
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Old 09-19-2000, 08:28 AM   #8
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6.5psi is too much for the needle valve seat springs in an AFB. Try 4psi.
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Old 09-19-2000, 08:28 AM
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