How to Adjust an Idle Screw on a Carburetor
The idle adjustment screw on your carburetor-equipped car or motorcycle controls the amount of air that is allowed into the carburetor continuously, keeping the engine alive when the vehicle is in neutral. Incorrect idle screw adjustments may lead to the vehicle dying at stop signs and lights, or the engine wearing itself by out running too high all the time. Keep your car or motorcycle in great running condition by fine-tuning the carburetor idle screw.
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Things You'll Need
- Owner's manual
- Philips screwdriver
- Flathead screwdriver
- Tachometer
- Basic wrench set
Instructions
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1
Use your owner's manual to locate the carburetor and the carburetor idle screw. Pop the hood of the vehicle and determine if a screwdriver or wrench will be needed to turn the idle screw.
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2
Install a tachometer if the vehicle does not already have one. A Tiny Tach is an inexpensive and easy option. Simply wrap the receiver wire of the Tiny Tach around one of the spark plug wires of the vehicle.
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3
Using the owner's manual that came with your vehicle, determine the correct idle speed for your engine. Some vehicles have a strict idle RPM (revoutions per minute) range, while others may have a wide range depending on altitude and average weather conditions.
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4
Turn on the vehicle and let it warm to running temperature. An engine runs differently when cold and therefore should be allowed to sit at least 10 minutes before any adjustments are made.
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5
Watch the tachometer while the engine runs. If the engine is running at too high an RPM measurement, loosen the idle adjustment screw until it falls to the correct speed.
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6
Tighten the idle screw if the engine runs at too low an RPM measurement. Continue tightening until the engine idles correctly.
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7
Take the vehicle for a test drive. Watch and feel for stuttering when starting from stops. When you return, you may fine-tune the carburetor idle screw depending on your driving style and road conditions.
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Tips & Warnings
If turning the idle screw does not allow for enough adjustment to the idle speed of the engine, there may be bigger problems with the vehicle. Have the vehicle inspected by a certified mechanic before driving any significant distance.
