If it's a slug you'll have a few possible problems. Dead carb - secondary vac actuator has got a split diaphragm or possibly the end of the actuator arm is disconnected (bad secondary vac unit is a common fault from age/wear and tear). Accelerator enrichment pump on the side of the carb has failed or has a blocked jet (another common fault - look down the throat on the primary side and open the throttle and if it's working you should see a shot of fuel from a small jet on the side of the throat). Dead auto choke (yet another common fault - if the choke has failed the choke butterfly won't open fully or possibly at all, tell tale layer of thick brownish grease around the underside of the wax pellet choke assembly). Non functioning vac advance unit on the distributor - poor acceleration, bit of pinging/engine knock from detonation. Dead ignition coil - more for acceleration, mid to higher rpm performance is poor, fuel economy is not great (if the coil is 15+years old, it has reached the end of it's serviceable life). Then there's the 'yeah, I know what I'm doing' engine tuner. Check plug gaps and condition, base timing, idle settings, throttle cable adjustment, throttle stop adjustment. You can screw up an engine tune pretty quick by trying to adjust base rpm by meddling with the distributor first and then taking a screwdriver to all the adjuster screws on the carb. It goes south very quickly...