Back to basics here.
Start with the simple stuff. FIrst off, is there fresh fuel in it?? If the tank is full and you didnt put it there, drain it out, and put in some fresh gas. If its old it will do exactly as youre describing. Second, go buy a cheapy seethrough fuel filter if you dont already have one. Install it, and make sure the fuel is clean. If you alsready have one, verify its not clogged.
If it starts and runs sometimes, the carb is probably good enough to run the car, dont tinker with it just yet.
Pull off your distributor cap, make sure the advance weights are there and they spin easily. If not, clean them off with a wirewheel, and put the tiniest amount of white lithium grease you possibly can to free them up. If its a points distributor, check your points gap. Its likely an HEI, so make sure the wires are all connected securely. Check the contacts inside the cap to make sure they are clean. If not, use a wirewheel and clean them. Check your plug wires, make sure they are ALL on the plug seated correctly.
Check your timing, set to factory. 6-8* initial should put you right in the mark.
We have to assume there is compression at this point, youve checked fuel, and ignition now. Try all of that, if it doesnt help, come back and let us know.
At this point you have bought some new gas, and maybe a fuel filter. If this doesnt solve your problem, or change the behaviour in any way, we can start looking at carb and ignition more closely.
Also, tell us what kind of carb it is. Post some pictures, pictures are worth a thousand words.