So many possible things could be causing this. I would start with the easy stuff. Make sure your valves are adjusted properly, better to be a little on the loose side to start than too tight. Check the timing to make sure the cam is in phase with the crank. Make sure the distributor is close to where it should be.

A vacuum leak can cause some goofy stuff. Try idling the engine while you spray starting fluid all around the gaskets on the intake manifold. If it speeds up while spraying part of it, you have a leak. Make sure all the vacuum ports are plugged or have the appropriate hose on them. All of us have forgotten to plug a hole or two on the intake or carb at one time or another.

Just start at ground zero and work up from there.

Don