A little more info is needed, such as the carb "list" number which is stamped into the front of the air horn, the piece that sticks up into the air cleaner. However, given that it's probably a "universal" Holley 600 like an O-1850 or an O-80457 here are some things to check:
1. First, eliminate the ignition system as a source of your problem. Hook up a timing light and run the wires out under the hood and duct-tape it to the wiper so you can see it flash from the driver's seat. Go out for a drive and try to duplicate the symptoms. If the light stops flashing while your symptoms occur then you know the problem is with spark delivery and not fuel delivery. If everything is good, then some things to look at follow:
a. Check the output of the fuel pump at the carburetor. You should have enough fuel flow to fill up a quart container in about 10 seconds of operation and at a pressure of between 5 & 6 psi.
b. If you have a fuel filter installed before the fuel pump, replace it with fuel line and install one AFTER the pump. Mechanical fuel pumps are notorious for difficulties sucking through partially plugged filters but have no problem pumping through them.
c. If you had decent flow and pressure, check the fuel filter installed at the carburetor inlet, if any. Replace as needed.
d. If you had poor flow but acceptable pressure, check the fuel cap to make sure the vent (if the system is vented) is functioning. You can typically pull air through the vent, but not push air out.
e. Let your sample in the jar sit for a half-hour or so. If you see water collecting at the bottom or bits of rust or dirt in the sample consider draining and inspecting or replacing the fuel tank &/or lines.
f. Check the fuel lines while the engine is running from the pump back to the tank. If you see any damp spots replace the bad line. Fuel pumps are good at pumping fuel but crappy at pumping air picked up through leaks in rubber or steel line.
g. Check the carburetor for external fuel leaks. Any leak is a reason to stop and just rebuild it now.
h. Check the float level (on a cold engine only) by placing damp (not wet) rags below the sight plugs on the side of the carburetor, remove them and start the engine. Fuel should be visible just at the bottom of the hole trying but not able to come out. Adjust the float by loosening the lock screw with a wide flat head screwdriver and then turning the adjustment nut, IIRC clockwise raises the fuel level and ccw lowers it. When the right level is found, hold the nut with the wrench and tighten the lock screw snugly. Stop the engine and clean up the spilled fuel.
Note: It's a good idea to have a friend standing by to shut down the engine and/or engage a fire extinguisher if needed. You can do the test with the engine off, but you need to devise a method to supply an uninterrupted flow of fuel to the carburetor.
i. If you still haven't found the source of your problem. check the operation of your accelerator pump(s), located under the float bowls. A movement of the throttle linkage should provide a decent squirt of fuel into the throttle bores.
j. Chances are your carburetor is equipped with "vacuum secondaries" - a diaphragm opens the secondary throttle plates at a low vacuum. If this isn't working your car will run like it's got a 2-barrel carb.
k. Still running like crap? Replace the power valve. On older Holley's without blowout protection, a good backfire could wreck the power valve. There isn't really a good way to test it so replacing it is the best way to eliminate it. There will be a number stamped on the valve to indicate its size.
l. Didn't work? Time to remove the carb and tear it down for a good cleaning and "rebuild". Chances are the float bowls are full of crap and something is plugging a passage. Rebuild kits contain gaskets, pump and secondary diaphragms and other little pieces plus an instruction sheet.
