I have a C2001-WK that does not auto shut off

A regulator controls the pressure in the air line leaving the compressor and does not affect when the compressor turns on or off.

The pressure switch monitors the pressure in the tank and turns the compressor motor on and off when the switch closes or opens in response to changes in the tank pressure. If the compressor does not shut off, it is possible the pressure switch has been set to a pressure level that is higher than the compressor is capable of attaining, thus it does not shut off.

The compressor is capable of developing 150 psi and is noted as having a "120 psi cut-in pressure". When you say it doesn't shut off, does that mean it will generate 150 psi or more of pressure and fails to shut off or it develops less than 150 psi and does not shut off.

If the compressor does not generate 150 psi, then it is probably somewhat worn out and not capable of developing enough pressure to meet the factory high pressure limit. I would try adjusting the pressure switch upper pressure limit down to 130 psi or less (less if the compressor will not develop 130 psi) and see if this solves your problem If it doesn't,

If the compressor will develop 150 psi or more, then try adjusting the high pressure limit to less than 150 psi. If you can't adjust the high pressure limit then the pressure switch is defective and needs to be replaced.