Could be fuel or advance timing, a couple easy checks to isolate.
1) with the engine idling, open the throttle by hand and verify the whole distributor rotates. If it does you're vacuum line is tight and the vacuum advance unit is good. If not troubleshoot the vacuum line and advance unit.
2) if #1 works, check the carbs accelerator circuit. Make sure the little accelerator rod is connected to the throttle linkage. With the engine OFF, remove the air cleaner, shine a flashlight down the carb and manually work the throttle to wide open, you should see a squirt of fuel. If not, either the linkage is off or the pump inside the carb wasn't installed correctly or damaged. disassemble and troubleshoot accordingly.
Good luck
