Basic 4 bbl carb question

Typically a carb with a high float (heavy float) will be hard to start or run rough, this can be a leaky needle valve also. Metering rods can also be stuck in the rich position flooding the engine at low speeds.. Your question was not clear if you are having problems or just need some info.. Some carbs have two floats (Motorcraft 4V) and one may be leaking. Holly is just a PITA when they get old.
I usually notice it in the idle. If it will idle at all, it's usually rough and hard to keep going(especially since the plugs will tend to load up very quickly). If you pull the plugs right after stalling, they'll probably be very dark if wet. As mentioned, a gas smell in the exhaust and/or under the hood is a good sign also. It the car has a cat, it may get hot enough to glow red. Depending on where the carb is in relation to it, this can actually create a very dangerous condition if a "leaky" carb drips gasoline onto the red-hot cat. Even the exhaust manifold(with no cat) can be hot enough to cause issues.
I have a Edlebrock Thunder Series 1806 carb. When I start her up my wife always complains about the gas smell which also happens sometimes when driving. Odd thing is that the car actually runs rather well with the occasional rough running. Plugs look fine but I am sucking gas at about 4-6 miles per gallon with a light foot. I get the fact that's its a big block but it seems its sucking and burning excessive gas. Other than that it runs like a beast with no hesitation or other issues.
Did you ever "tune" the carburetor (jets, metering rods, step-up spring, secondary air valve) for your specific 402, intake manifold, cam, and ignition combination or did you just bolt it on and go? You should be getting about double the gas mileage that you are getting now. It sounds to me like this needs to be done. Also, how much fuel pressure do you have? 5-6 psi is best, 6.5 psi is MAX, if you have more fuel pressure than this you found one of your problems and you need to add a fuel pressure regulator.
Did you buy the car in it's current configuration or did you install the carburetor (and do other modifications) yourself? Does the car have a stock OEM intake manifold? If so, was the correct Edelbrock #2696 adapter plate used? If not, that is one of your problems right there.
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sounds like. 1. a bad float has a hole , letting fuel in. 2. dirt on needle and seat. 3. missed adjusted float. should be 7 / 32. 4. a bent float touching the wall. dont bother to check the float DROP . as the float will hit the bottom of the bowel be fore it causes any trouble. unless it way to high. the factory setting for float drop is 3 / 4