The Ford Barn

ford38v8 · 08-31-2025, 08:16 PM

Kev, A small correction here that may give you an insight on your adjustments: The "mixture screws" are merely IDLE mixture screws, not to be adjusted for anything but idle. Since you do have a lumpy cam and need a higher idle speed, they will need to provide more fuel. Locate instruction for adjusting them correctly with your cam and that should help.

EDIT: This might be the first ChatGTP advice on the Fordbarn:.

Step-by-Step Idle Adjustment (Holley 94, Lumpy Cam)

Warm it up

Run the engine until it’s at full operating temperature.

Make sure choke is fully open.

Baseline settings

Gently seat both idle mixture screws (don’t force).

Back each screw out 2 full turns.

Set the idle speed screw so the engine will just stay running (probably around 650–750 rpm for a lumpy cam).

Hook up a vacuum gauge (if you have one)

Plug it into a full-manifold vacuum port.

If not, just go by ear and feel.

Adjust one side

Pick one idle screw.

Turn it in slowly until the engine just starts to stumble or rpm drops.

Now turn it out slowly until rpm peaks (or vacuum is strongest).

Leave it there.

Adjust the other side

Do the same with the second idle screw: in until stumble, then out to the sweet spot.

Re-check idle speed

If rpm is too high or too low, use the idle speed screw (on the throttle arm) to bring it back to a steady idle.

Expect around 700 rpm as a realistic goal with a lumpy cam (stock would be lower).

Final tweak

Go back and make a small touch-up on each idle screw (⅛ turn either way) to get the best compromise: highest steady rpm, strongest vacuum, and smoothest response when you crack the throttle.

08-31-2025, 08:16 PM	#11
ford38v8 Senior Member Join Date: Jul 2011 Location: SF Bay Area Posts: 7,634	Re: Ignition Issues, Crab distributor Kev, A small correction here that may give you an insight on your adjustments: The "mixture screws" are merely IDLE mixture screws, not to be adjusted for anything but idle. Since you do have a lumpy cam and need a higher idle speed, they will need to provide more fuel. Locate instruction for adjusting them correctly with your cam and that should help. EDIT: This might be the first ChatGTP advice on the Fordbarn:. Step-by-Step Idle Adjustment (Holley 94, Lumpy Cam) Warm it up Run the engine until it’s at full operating temperature. Make sure choke is fully open. Baseline settings Gently seat both idle mixture screws (don’t force). Back each screw out 2 full turns. Set the idle speed screw so the engine will just stay running (probably around 650–750 rpm for a lumpy cam). Hook up a vacuum gauge (if you have one) Plug it into a full-manifold vacuum port. If not, just go by ear and feel. Adjust one side Pick one idle screw. Turn it in slowly until the engine just starts to stumble or rpm drops. Now turn it out slowly until rpm peaks (or vacuum is strongest). Leave it there. Adjust the other side Do the same with the second idle screw: in until stumble, then out to the sweet spot. Re-check idle speed If rpm is too high or too low, use the idle speed screw (on the throttle arm) to bring it back to a steady idle. Expect around 700 rpm as a realistic goal with a lumpy cam (stock would be lower). Final tweak Go back and make a small touch-up on each idle screw (⅛ turn either way) to get the best compromise: highest steady rpm, strongest vacuum, and smoothest response when you crack the throttle. __________________ Alan Last edited by ford38v8; 08-31-2025 at 08:37 PM.