Older vehicles, like your 1973 VW Beetle, were not designed to use fuels with ethanol. Ethanol can damage fuel lines and seals, and it can cause problems with the engine.
If you want to use ethanol in your vehicle, you should consider having the fuel system upgraded. The fuel system needs to be modified to make it compatible with ethanol.
It's always a good idea to consult your owner's manual or a qualified mechanic before making any changes to your vehicle's fuel system.
