In regular fuel systems, gasoline is supposed to pass through the jets of the carburetor, vaporize and mix with air. This is all fine when it's working properly but when the carburetor floods, there's a real fire hazard because gasoline is actually flooding out of the carburetor. Many confuse flooding with a starting problem when flooding actually occurs when the vehicle is being driven or has been stopped and shut off. Troubleshooting a Holley carburetor that's flooding may seem difficult at first, but you can rapidly diagnose the problem by following a series of diagnostic steps.
Inspect the charcoal canister, if so equipped, to ensure that it is not saturated with gasoline.
Inspect the vent valve to ensure it is working correctly.
Inspect the vent hoses to ensure that they're not kinked.
Inspect the vent system to ensure that there are no defective check valves.
Inspect the gas tank vent and gas cap vent to ensure that they are not blocked.
Inspect all gas lines to ensure that they are not too close to a heat source such as an exhaust manifold or radiator hose. Excessive heat causes the fuel to expand and be forced past the needle and seat.
Inspect the heat riser to ensure that it is not stuck in the closed position.
Remove the Holley carb from the vehicle, following the instructions in the repair manual. Shake the carburetor hard a few times. This will normally cure any problems inside the carburetor, such as foreign matter in the needle valve or another part that is not functioning properly. If this does not cure the problem, open up the carburetor and inspect the needle and seat to ensure that there is no dirt stuck between the needle and seat.
Connect a tachometer to the engine. Ensure that the engine idle is set to factory specifications.
Inspect the idle solenoid to ensure that it is working properly. Ensure that there is power to the solenoid and that it is grounded. Inspect the solenoid for dirt or foreign matter that is stuck in the solenoid or the passages to it.
Measure the fuel pressure with a fuel pressure gauge mounted between the fuel pump and carburetor. Ensure that fuel pressure is steady and within factory specifications.
Inspect the float chamber to ensure that the float has not sunk or become heavy with fuel that is late again.
