Possible Causes and Solutions
1. Fuel Vaporization (Vapor Lock)
When the fuel in the carburetor or fuel lines vaporizes due to high engine temperature, it can cause the engine to stutter and stall. This issue typically resolves itself once the engine cools down, which aligns with your observation that the Jeep won’t start for about 30 minutes.
See our page for percolation.
Solution:
- Insulate Fuel Lines: Wrap the fuel lines with heat-resistant material to keep the fuel cooler.
- Install a Heat Shield: Place a heat shield between the carburetor and the engine to reduce the heat transferred to the fuel.
- Reroute Fuel Lines: Ensure fuel lines are not running too close to hot engine components.
2. Fuel Pump Issues
If the fuel pump is failing or not delivering enough fuel when the engine is hot, it could cause the symptoms you're describing.
Solution:
- Inspect the Fuel Pump: Check for any signs of wear or damage. Ensure the pump is delivering a consistent fuel supply. Test the fuel pump for 4-4.5 lbs.
- Electric Fuel Pump: Consider installing an electric fuel pump, which can be more reliable and less prone to vapor lock. If you do this be sure to add a regulator. Electric fuel pumps pump too much pressure.
3. Carburetor Problems
The carburetor itself might have issues that become pronounced when the engine is hot. This can include float level problems, clogged jets, or a sticking needle valve.
- Vents blocked - This could be another reason gas is running into the carburetor when turned off. Any vents that are blocked will cause a vacuum effect in the float bowl.
- Check the main discharge. When hot turn off the engine and look down the carburetor. Fuel should not be dripping into the venturi area. If it is then might be the discharge check ball leaking, or plugged off vent.
- The gas cap should be a vented type. If you remove the gas cap and you hear a swoosh of air then the cap is probably not vented.
Solution:
- Carburetor Rebuild: Rebuild the carburetor, ensuring all components are clean and functioning properly. Pay special attention to the float level and needle valve.