[rhandwor]

As the engine is running spray carb cleaner along the intake manifold if the idle smooths out replace the gasket. Spray around the base of the carb if smooths out replace gasket. Use vise grips and pinch off hose to vacuum booster. If runs much better get a rebuilt unit. Clean pcv and hoses from carb.
To check timing chain rotate engine counter clockwise to top dead center. Pull the dist cap and mark rotor and dist base with white out where they meet. Turn the engine clockwise with a person watching the rotor. Stop when the rotor starts to move. Over 15 to 20 degrees you need a new timing chain.
If the chain is good retime the engine. Check that the vacuum advance advances the timing first. Then you need to plug the hose to the vacuum advance to time the engine.
I would inspect the cap and rotor and ohm all plug wires while I was working on it.
You may also need to install a carb kit.
A worn valve guide and camshaft will cause a mis and also backfire.