* Vacuum Leaks: This is the MOST likely culprit. A vacuum leak can drastically affect idle. Even a tiny leak can cause the engine to stall because the idle mixture is thrown off. Check *everywhere* for cracks or loose connections in:
* Intake Manifold Gaskets: A very common source of vacuum leaks on these cars.
* Vacuum Lines: Inspect all vacuum lines for cracks, holes, or loose connections. Pay close attention to lines connected to the carburetor, brake booster, and emission controls. Replace any suspect lines.
* Power Brake Booster: A leak here will draw a significant amount of vacuum.
* Manifold to Carb Gasket: A leak here is a frequent problem.
* Idle Air Control (IAC) Valve (if equipped): While less common on older vehicles, some '81 Camaros might have a rudimentary version of an IAC. If it's sticking or malfunctioning, it won't provide the correct amount of air to maintain idle. Check for cleanliness and smooth operation (if applicable).
* Choke System: If the choke isn't opening fully when the engine is warmed up, it will starve the engine of air, causing a rough idle or stalling. Make sure the choke is functioning correctly and is fully opening when the engine is warmed up.
* Fuel Delivery Issues: Although you've had the carb rebuilt, consider these less likely but still possible issues:
* Fuel Pump: A weak fuel pump may not deliver enough fuel at idle.
* Fuel Filter: A clogged fuel filter will restrict fuel flow.
* Clogged Fuel Lines: Restricted fuel flow.
* Ignition System: While less likely given the RPM dependency, weak spark at idle could contribute.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect all vacuum lines, the intake manifold, and carburetor for any visible cracks, loose connections, or other signs of damage. Use a propane torch (carefully!) to test for vacuum leaks by listening for a change in engine RPM as you pass the flame near suspected leak locations. *Do this only in a very well-ventilated area; propane is flammable.*
2. Vacuum Gauge: Connect a vacuum gauge to the manifold vacuum port. A steady vacuum reading is essential for proper idle. Fluctuations or low readings indicate leaks.
3. Check Idle Mixture Screws: With the engine running, carefully adjust the idle mixture screws (small screws typically found on the carburetor's sides) slightly. This requires a steady hand and some mechanical aptitude – consult your carburetor's manual. Improper adjustment can cause damage. Only do this if you have experience with carburetor adjustment.
4. Clean the Carb Thoroughly (Again): Even if it's been rebuilt twice, there might be a lingering issue. Check the passages and make sure everything is clean and free from debris.
5. Check and Clean IAC valve (if equipped): If your car has an IAC, clean it with carburetor cleaner.
If you've checked all of the above and the problem persists, it's best to seek help from a mechanic specializing in carburetors or older vehicles. They'll have the tools and expertise to diagnose more complex issues. Trying to troubleshoot further without the proper tools and knowledge could damage the engine.
