All '81 CB650s came with VB44A carbs, which will need to be rebuilt. Rebuild kits are relatively widely available, though folks do not like aftermarket brass (jets). They're easy to completely rebuild, but have some finnicky parts that can cause confusion if its your first time (looking at you, press-in slow jets). The floats are the non-adjustable variety, so if they're shot then replacements are ~$20 a pop. Carb insulators will need to be replaced as well since they'll be hard as rocks.
Ignition is transistorized, so no points to worry about.
Make sure the fuel tank is either clean inside or has very little rust. No leaks. Replacing the tank will be costly since you'll be at the whim of used tanks of the same year/model unless you want to perform modifications.
Otherwise everything is straight forward. Make sure the motor has compression, do the regular maintenance, get new tires & chain/sprockets and let her rip.
