* Ignition Timing: The most probable culprit. Incorrect ignition timing can cause the engine to run poorly or stall under load (acceleration). The timing needs to be advanced to deliver the spark at the right moment when the engine is working harder.
* Fuel Delivery Problem (despite new parts): While you've replaced the fuel filter and carb, there might still be an issue:
* Clogged carburetor jets: Even a new carb can have partially clogged jets. A thorough cleaning of the carburetor, beyond just replacing it, might be necessary.
* Fuel pump issue: A weak fuel pump might deliver enough fuel at idle but struggle to keep up when the engine demands more fuel under acceleration. The pump might need replacement or inspection.
* Vacuum leaks: A vacuum leak can starve the engine of fuel under load. Inspect all vacuum lines and the intake manifold for cracks or loose connections.
* Distributor issues (if applicable): If your vehicle has a distributor, problems with the mechanical advance mechanism inside could lead to improper ignition timing under acceleration.
Troubleshooting Steps:
1. Check Ignition Timing: This is the *most likely* problem. Have the ignition timing checked and adjusted by a mechanic or using a timing light if you're familiar with the procedure.
2. Inspect the Fuel System Again: Look closely at the fuel lines for cracks or kinks. Carefully examine the carburetor (again!) for any signs of debris or clogging in the jets. Consider checking fuel pressure if possible.
3. Check for Vacuum Leaks: Spray carburetor cleaner (or starting fluid, cautiously!) around all vacuum connections and the intake manifold while the engine is running. A change in engine speed indicates a leak.
4. If it has a distributor: Have it inspected for proper advance operation.
Important Note: Without knowing the make, model, and year of the vehicle, giving more specific advice is difficult. If you're uncomfortable working on the vehicle yourself, taking it to a qualified mechanic is recommended.
