Starts then dies after 5-10 seconds - carb spitting out gas

[70pumpkin]

Can't wait to switch to efi, but in the meantime, my car keeps on dying and I don't know why.  Car starts right up but after 5-10 seconds (in fast idle), it dies and spits out gas from the throat.  I've tweaked the timing and manually adjusted the air/fuel mixture screws, but get the same results.  Carb is an old 2-bbl Holley Economaster.

I suspect it's a float or gasket issue, but I really don't know much about carbs so looking for some help...

[Chryco Psycho]

there is a stuck float or dirt in the needle & seat holding the valve open , you need to tap on the carb to see fi the dirt willdislodge or take the carb apart & clean it

[Rich G.]

Will it stay running if you spray carburetor cleaner in it? If it does it's starving for gas like Chryco said or you have a major vacuum leak,

[usraptor]

I agree with Chryco, the float is stuck in the open position and your are flooding the engine.

[Rich G.]

Chryco is right if the float is stuck and it's flooding out. Or am I misreading what he's describing. You would think it would be leaking gas out of the throttle shaft and a ton of black smoke if it was running that rich. Look in the carb when it shuts off. Is fuel still running in? 

[YellowThumper]

I vote for bad float. Pull it and it should weigh almost nothing. They do go bad and soak fuel. Get heavy and flood the motor.