Vapor lock is pretty much a thing of the past for most people. Vapor lock occurs when the vapor pressure of the fuel is higher than its surroundings. The gasoline in the fuel lines will actually boil creating a vapor of gasoline which a fuel pump can not handle. Today's cars have fuel pumps in the fuel tank where they push the fuel under pressure to the engine. This is wonderful if you own a new car.
In older cars with sucking fuel pumps near the engine, the pressure in the fuel line from the tank is reduced by the fuel pump drawing fuel from a tank at the other end of the car. When this gas starts to get hot, it will actually boil into vapor. Vapor lock is usually the result of high altitude and high temperatures. Vapor lock can occur at any altitude due to excessive heat, but it is more common at higher altitudes because gas at high altitudes vaporizes at a lower temperature. The resulting gas and air mixture can reduce or even stop the flow of gas to your engine.
Symptoms that your car is suffering from vapor lock is a loss of engine power or an engine that will suddenly not start. Vapor lock is most common when you turn off your car on a hot day then try to start it up again a few minutes later. To reduce the chance of vapor lock, avoid running the air conditioner when you don't really need to. At the first signs of power loss, shift your car into neutral and rev the engine slightly. Always use low gear when climbing steep hills.
If your engine has become a victim of vapor lock, here are a few things you can try:
Loosen the gas cap slowly.
Remove the air cleaner cover and hold open the choke flutter valve in the carburetor with a screwdriver. Look out for backfires.
Start the engine, holding the gas pedal all the way to the floor.
If these steps don't work, let the motor cool at least 30 minutes before trying to start the car.
The only thing that truly cures vapor lock is a cool engine.
"As you said modern cars seldom suffer from vapor lock but in addition to the pump location the modern systems operate at a much higher pressure and the systems have bypass regulators. The higher pressures used keeps the fuel from vaporizing and the bypass regulator circulates cooler fuel through the system constantly.
On older cars a bypass regulator can be installed near the carburetor and excess fuel is routed back to the tank and cooler fuel is constantly drawn from the tank. As the fuel does not sit in the fuel line as long it is generally cooler and less prone to vapor lock. Installing an electric pump near the tank in the rear of the car also helps. Installing the pump near the tank pushes the fuel at a pressure of 4 psi or so above atmospheric pressure versus pulling it at a pressure of 4 psi or so to an engine mounted pump ie look up the vapor pressure of gasoline at 10.5 psi versus 18.5 psi (absolute)." Hope this helps try putting thermo wrap around the headers to keep the heat in the tube and out of the engine compartment. Eventually your starter will also start failing so put a heat shield around it to protect it. Headers add power but they add headaches also. I have the ceramic coated ones and still have the heat shield by the starter. Good Luck!
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