You have probably heard that vehicles made before the advent of electronic controls – electronic fuel injection and transistorized ignition, specifically – would not be disabled by an electromagnetic pulse (EMP) such as are emitted by nuclear detonations.

Mechanical things like carburetors and points are kind of like the Honey Badger, who is said to be deterred by nothing. Vehicles with mechanically injected diesel engines are the apotheosis of this invulnerability. They don't even need a working alternator/generator to run. Much less a battery to start. Roll it down the hill, let the clutch out and it'll run until you shut it off. They can also burn fuels other than diesel when diesel isn't available, such as vegetable oils.

Gas-engined vehicles made through the early-mid 1980s will usually have a carburetor rather than fuel injection, but most of the models made after 1980 have crude computer controls. They also usually have transistorized ignition systems. An EMP would likely disable them. The good news is the electronics are simple and the computer control of the carburetor can be deleted by replacing the electronically controlled carburetor with an essentially identical older one that doesn't have any electronic controls. It will "bolt on" in place of the original with few if any modifications. Things such as throttle and transmission kickdown linkages (for automatic-equipped cars) usually connect without having to alter anything and there's usually no electronic fuel pump, either. These cars tend to run better with the non-computer-controlled carbs anyhow and they are certainly easier to tune/service, so making the swap just makes sense – irrespective of the EMP issue.