* Idle mixture screw adjustment: The idle mixture screw(s) are crucial for proper idling. They control the amount of fuel entering the engine at idle. If they're improperly adjusted (too lean or too rich), the engine will stall or run poorly at idle. This is the *most likely* cause. The adjustment needs to be very precise.
* Idle speed screw adjustment: The idle speed screw sets the engine speed at idle. If it's set too low, the engine doesn't get enough fuel to stay running. If it's set too high, it might run but not smoothly.
* Vacuum leaks: A vacuum leak anywhere in the intake manifold or carburetor gasket will drastically affect idle. Even a small leak can make idling difficult or impossible.
* Choke issues (partially stuck): Although less likely with a brand new carburetor, if the choke isn't fully retracting, it can starve the engine of air at idle.
* Clogged idle jets: While rare in a *brand new* carburetor, it's possible a small piece of debris might have blocked an idle jet during installation.
* Incorrect carburetor installation: Improper installation of the carburetor itself, such as a faulty gasket or incorrect throttle linkage adjustment, can cause problems.
Troubleshooting Steps:
1. Check the Idle Mixture Screw(s): Consult your carburetor's instructions or a service manual for the proper adjustment procedure. This usually involves turning the screw in small increments while observing the engine's idle speed and smoothness. Start by making small turns in either direction and find the point where it runs smoothest.
2. Check for Vacuum Leaks: Use a propane torch (with the propane turned *off*) to carefully check for leaks around the carburetor and intake manifold. If a leak is present, the engine will briefly speed up when you bring the unlit torch near the leak.
3. Inspect the Choke: Ensure the choke is fully opening when the engine is warmed up.
4. Verify Idle Speed Adjustment: Adjust the idle speed screw to a slightly higher idle than normal as a temporary test and see if the engine stalls less.
5. Recheck Installation: Double-check all connections and gaskets to ensure the carburetor is properly seated and sealed.
6. Check Fuel Delivery: Verify that fuel is properly flowing to the carburetor.
If none of these steps solve the problem, you may need to consult a qualified mechanic familiar with carburetor systems. It's possible there's a more serious internal issue with the new carburetor, though that's less likely. Remember safety first, and if you're not comfortable working on a car's engine, don't hesitate to call a professional.
