What can cause older engine to misfire and have lack acceleration?
Sounds like it needs a full tune up.
Being '71 it's still got a points ign. system. Points wear, burn and crack alot. If you can, swap it to an elec. dizzy.
New plugs, cap, rotor, plug wires, points if staying with them, check and set timing, adjust carb for highest vac readings on a vac gauge., new fuel filter
The carb may be in need of a rebuild as well