Here's a breakdown of more likely culprits, working from most to least likely:
High-Probability Issues:
* Fuel Delivery: This is the most common cause.
* Fuel Pump: A failing fuel pump may not be delivering enough fuel, especially under load (acceleration or hills). It might work intermittently, leading to shutdowns. Listen for the pump whirring when you turn the key on – it should run for a few seconds.
* Clogged Fuel Filter: A dirty fuel filter restricts fuel flow. This is a cheap and easy check – replace it.
* Fuel Lines: Cracks or kinks in the fuel lines can restrict or interrupt fuel flow. Inspect the lines visually for damage.
* Carburetor Issues (Beyond the Rebuild): Even after a rebuild, the carburetor could have problems:
* Fuel level: Incorrect fuel level in the float bowl.
* Clogged jets: Small passages in the carburetor can easily clog.
* Accelerator pump: This provides extra fuel during acceleration; a malfunction can cause stalling.
* Ignition System:
* Distributor Cap and Rotor: These components wear over time and can cause intermittent sparking, leading to engine shutdowns. Inspect for cracks, corrosion, or burned areas.
* Ignition Coil: A weak or failing coil can't provide enough voltage for consistent sparking.
* Worn Wires: Check all high-voltage ignition wires for cracks, fraying, or loose connections. A simple visual inspection can often find problems.
Less Likely, But Possible Issues:
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's operation. Listen carefully for unusual hissing sounds near the intake manifold.
* Temperature Sensor: A faulty temperature sensor might provide incorrect readings to the computer (if equipped, some 78 models might have rudimentary electronic components), resulting in improper fuel mixture and stalling.
* Alternator: While less likely to cause an immediate shutdown, a failing alternator can drain the battery, eventually leading to a stall. Check the battery voltage with a voltmeter.
How to Approach Troubleshooting:
1. Start with the easy stuff: Replace the fuel filter. This is cheap and often solves the problem.
2. Check fuel pressure: If you have the tools, measuring fuel pressure will tell you if the pump is delivering enough fuel.
3. Inspect visually: Carefully examine fuel lines, distributor cap, rotor, and ignition wires for obvious damage.
4. Listen for unusual noises: Pay close attention to any hissing sounds (vacuum leaks) or unusual engine noises.
5. Choke Adjustment (Least Likely): The choke is for cold starting. If it's adjusted improperly, it might cause rough running *when starting cold*, not shutting off *while driving*. This adjustment usually involves screws on the carburetor itself and requires some mechanical knowledge and potentially specialized tools. If you're not comfortable, leave it alone.
Recommendation:
Unless you have significant experience working on carburetors and ignition systems, taking it to a mechanic familiar with older vehicles is likely the most efficient solution. Diagnosing intermittent problems like this can be time-consuming. The cost of a proper diagnosis will likely be less than the cost of replacing parts based on guesses.
