* Carb Issues: This is the most probable cause. The carburetor needs to provide the correct fuel/air mixture at idle. Problems could include:
* Dirty carburetor: Accumulated dirt, varnish, and debris can clog jets, passages, and the idle circuit, leading to a lean fuel mixture at idle. A thorough cleaning or rebuild is often necessary.
* Clogged idle air/fuel jets: These tiny jets are critical for idle operation. A clog will drastically affect the mixture.
* Vacuum leaks: Leaks in the intake manifold, vacuum lines, or the carburetor itself can draw in unmetered air, disrupting the air/fuel ratio and causing erratic idle or stalling.
* Faulty choke: If the choke isn't working correctly, it can prevent the engine from getting enough fuel when cold, leading to stalling. This is especially likely when the engine is cold or if the problem is more pronounced after a cold start.
* Incorrect float level: If the float level in the carburetor is off, it could be flooding or starving the engine of fuel.
* Worn throttle shaft: A worn throttle shaft can cause vacuum leaks or incorrect throttle plate positioning.
* Ignition System: A weak spark can also contribute:
* Worn distributor cap and rotor: These components degrade over time and can cause misfires, especially at idle when the spark needs to be reliable.
* Worn spark plugs or plug wires: These can cause a weak or intermittent spark, leading to misfires.
* Failing ignition coil: A weak coil produces a weak spark.
* Ignition timing: Incorrect timing can disrupt the engine's smooth running, leading to stalling.
* Fuel System:
* Clogged fuel filter: A clogged filter restricts fuel flow, causing problems at low engine speeds.
* Fuel pump issues: A weak or failing fuel pump might not provide sufficient pressure at idle.
* Other Potential Issues:
* PCV valve: A faulty PCV (Positive Crankcase Ventilation) valve can affect the vacuum system and cause idle issues.
* EGR valve: The EGR (Exhaust Gas Recirculation) valve could be sticking or malfunctioning.
Troubleshooting Steps:
1. Check for obvious vacuum leaks: Visually inspect all vacuum lines and connections for cracks or loose fittings. Use a propane torch (carefully and away from flames!) near suspected leak areas to see if the engine RPM changes; a change indicates a leak.
2. Inspect spark plugs and wires: Check for fouling, cracking, or corrosion. Replace as needed.
3. Check the distributor cap and rotor: Look for cracks, arcing, or corrosion.
4. Check the fuel filter: Replace it if it's dirty or old.
5. Start with the carburetor: This is the most likely culprit. A good cleaning or professional rebuild is often the solution.
6. Check the fuel pressure: If you have a fuel pressure gauge, check the fuel pressure at the carburetor.
7. Check the ignition timing: A mechanic should do this.
If you're not comfortable working on the carburetor yourself, it's best to take it to a mechanic specializing in older vehicles, especially those with carbureted engines. Trying to diagnose this without experience can lead to further damage or frustration. A detailed description of the symptoms (e.g., how long it runs before stalling, whether it stalls only when hot or cold, etc.) will help a mechanic narrow down the possibilities.
