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Adjusting the Computer Controlled Feedback Carb: Part 3

Technically Speaking: Rich Stop and Lean Stop Settings on the Corvette Computer Controlled Feedback Carburetor

James Berry Oct 10, 2017
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This month I thought we were going to finish this series on adjusting the computer controlled feedback carburetor but it looks like it will take one more installment to complete this series. I have received several e-mails and questions, which has led me to add additional information.

This month we will cover the base rich stop and lean stop settings.

Rich Stop and Lean Stop Setting

If adjustment of the rich stop or the lean stop is necessary there is a tamper-resistant plug that will need to be removed.

This procedure is the same as we covered last month when removing the throttle position sensor (TPS) tamper-resistant plug. To review, drill a small hole in the aluminum plug covering rich stop or lean stop adjustment screw; only drilling deep enough to start a self-tapping screw. Start a self-tapping screw in into the drilled hole in the plug, turning screw in only enough to ensure good thread engagement so you do not damage the adjustment screw. Pry against screw head to remove the plug.

If you are removing the carburetor air horn for any reason, such as replacing the mixture control solenoid or the throttle position sensor simply take a hammer and a small punch and tap out the tamper-resistant plug covering the rich stop or the lean stop adjustment screws after the air horn has been removed. After all adjustments have been made and you are happy with how the vehicle is running, reinstall the tamper-resistant plugs to help lock in your final adjustments and keep any debris from getting into the carburetor. This can be done after your test drive.

Rich Stop Calibration Procedure

Rich Stop Adjustment 2/3

Positioned in the top of the carburetor near the main venturi is the rich stop, it defines how far the metering rods can travel out of the main jets when the mixture is driven rich. The adjustment screw is located on top of the carburetor next to the idle air bleed valve.

All settings are to be made with the engine off.

You will need to check your service manual for the correct rich stop setting.

With the air horn installed and the rich stop tamper-resistant plug removed from the air horn. The most common setting for the rich stop is to gently turn it counterclockwise until it stops (bottoms out).

Next, turn the clockwise out 2.5 complete turns you can use this as a base setting. This should be close if you do not have the gauge tool.

Rich stop setting, using the gauge tool; with the air horn installed and the rich stop tamper-resistant plug removed from the air horn. Gently turn it counterclockwise until it stops (bottoms out).

Insert gauge in vent hole and turn stop screw clockwise until total solenoid plunger travel is 3/32-inch.

Lean Stop Calibration Procedure

Lean Stop Adjustment 3/3

The lean stop is located in the main body of the carburetor. If you are adjusting it without dissembling the carburetor you will access it through the air horn about one inch in front of the rich stop adjustment screw. The lean stop defines how far down into the main jets the metering rods travel to reduces fuel flow and drive the air/fuel mixture lean.

All settings are to be made with the engine off.

With the air horn installed and the lean stop tamper-resistant plug removed from the air horn. The most common setting for the lean stop is to gently turn it clockwise until it stops (bottoms out).

Next, turn the counter clockwise out 3-1/2-turns complete turns you can use this as a base setting.

Lean stop setting, using the gauge tool; with the air horn installed and the lean stop tamper-resistant plug removed from the air horn. Gently turn it clockwise until it stops (bottoms out).

Insert modified float gage down D shaped vent hole. Press down on gage and release, observing that gage moves freely and does not bind.

With gage re-leased (solenoid in the up position), read and record the mark on the gage in inches that lines up with top of air horn casting upper edge.

Then, lightly press down on gauge until it bottoms out (solenoid in the down position). Record in inches mark on gage that lines up with top of air horn casting.

Subtract gage up dimension from gage down position and record difference. The difference is total solenoid travel.

The total solenoid travel should be between 2/32-inch to 4/32-inch.

After performing these settings proceed to idle air bleed valve adjustment.

Next month I promise we will finish this series with adjusting the air bleed screw in the top of the air horn, removing the plugs to gain access for adjusting the air/fuel mixture screws, what order you should use when making the settings, and finally how to use dwell to fine-tune the carburetor.

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