holley carb question

If it's pouring gas into the engine ( not ON the engine) then you've got a stuck float or blown power valve. For stuck float try tapping on the float adjuster screw at the top center of each bowl with a screw driver handle while the engine is running. If that doesn't stop it, then you'll need to remove the bowl(s) and replace the needle & seat assembly(s). That would also be a good time to replace the power valve as well. To check the condition of the power valve, unscrew it from the metering block and suck on the smooth side, if the diaphram in it is good, you'll be able to feel the piston in it move back and forth while sucking on it. If it's pouring the gas ON the engine from underneath the primary bowl, then the accellerator pump diaphram is busted, this will also require removing the primary bowl and removing the pump cover ( 4 screws) to get to the diaphram. You would do well to pick up a Holley "Quick Kit" to get all the parts you'll need. The 3310 part# you listed is the number you'll need to get the right kit. This is the "list" number. A 3310 carb is a 750 cfm vacuum secondary 4 bbl carb. The earliest 3310's were 780's.

it sounds like there's a particle of something in the needle & seat, blocking it from closing. it thinks the bowls need fuel when they dont.
I'd guess it sucked up a small piece of rust from the tank.
Determine if its the front or rear venturies.
Take that needle & seat out of the proper bowl by loosening lock nut (5/8" wrench?) then backing out the needle & seat using a big flat blade screwdriver. (They are located on the top of each bowl.)
How far that screw is threaded in determines the float level, you may want to count how many turns it takes to remove it, so when you re-install it you can get it close to where it was before.

Take needle & seat assy out, inspect and blow it clean , should have a good rubber tip for sealing. Replace or clean as needed.
Re-install, and re-set float bowl levels by turning the screw in/out and lock it with the nut when done.