1. Idle speed screw: The idle speed screw, which is located on the side of the carburetor, is used to adjust the engine's idle speed. Turn the screw clockwise to increase the idle speed and counterclockwise to decrease it.
*NOTE:* Turn the idle speed screw out and back in 1-1/2 turns as a starting point. Next, turn the idle mixture screw in and back out 1-1/2 turns as a baseline setting. Start the engine. Using a screwdriver, turn the idle speed screw to achieve 850-950 RPM. Recheck and readjust the idle speed as necessary to keep it within this range when warm.
2. Air leaks: Air leaks can cause the engine to run lean and idle poorly. Check the following areas for leaks:
- Intake manifold gasket
- Carburetor base gasket
- Throttle shaft seals
- Vacuum hoses
3. Vacuum leaks: Vacuum leaks can also cause the engine to run lean and idle poorly. Check the following areas for leaks:
- Brake booster hose
- PCV valve
- Vacuum advance line
- EGR valve (if equipped)
4. Fuel filter: A clogged fuel filter can restrict fuel flow to the carburetor, causing the engine to run lean and idle poorly. Replace the fuel filter if it is clogged.
5. Fuel pressure: Low fuel pressure can also cause the engine to run lean and idle poorly. Check the fuel pressure and make sure it is within specifications.
6. Spark plugs: Worn spark plugs can cause the engine to misfire and idle poorly. Replace the spark plugs if they are worn.
7. Spark plug wires: Bad spark plug wires can also cause the engine to misfire and idle poorly. Replace the spark plug wires if they are bad.
8. Distributor cap: A cracked or damaged distributor cap can cause the engine to misfire and idle poorly. Replace the distributor cap if it is cracked or damaged.
9. Distributor rotor: A worn distributor rotor can also cause the engine to misfire and idle poorly. Replace the distributor rotor if it is worn.
10. Fuel jets: The fuel jets in the carburetor are responsible for metering fuel to the engine. If the fuel jets are clogged, the engine will run lean and idle poorly. Clean the fuel jets if they are clogged.
11. Fuel mixture screw: The fuel mixture screw, which is located on the side of the carburetor, is used to adjust the air/fuel mixture. Turn the screw clockwise to lean out the mixture and counterclockwise to richen it.
*NOTE:* Turn the idle mixture screw in and back out 1-1/2 turns as a baseline setting. Start the engine. Using a tachometer, adjust the idle mixture screw to achieve a fast idle (1,500-2,000 rpm). Recheck and readjust the idle speed as necessary to keep it within this range when warm.
If you have tried all of these things and the engine is still idling poorly, you should take it to a qualified mechanic for further diagnosis.
