Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Cars With Throttle Stopscrew
If adjustment required to warm up engine, set both idle mixture screws 1 1/2 turns from a lightly seated position. With engine at normal operating temperature (choke valve wide open and fast idle inoperative so that engine idles at hot or slow idle speed), set throttle stopscrew for correct idle speed (see "Specifications "), Adjust both idle mixture screws equally for smooth idling and maximum engine RPM. Readjust idle speed and recheck idle mixture screw settings. See special notes below.
1959-64 CHEVROLET & CHEVELLE NOTE - Turn adjusting screw in until engine is moderately rough (slight vacuum and RPM drop), then turn screw out 1/4-turn to enrich mixture. Adjust both screws alike.
BUICK NOTE - Turn each adjusting screw in until engine begins to lag or run unevenly from lean mixture, then turn screw out until engine begins to roll from rich mixture. Finally turn screw in just enough to produce smoothest operation. Adjust both screws alike.
OLDSMOBILE NOTE - After adjusting idle mixture for smoothest idle with highest RPM, turn each adjusting screw out 1/4 turn (vacuum and RPM will drop slightly).
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.