My 33 gallon air compressor will at start build up to 120 psi and shut off, after use and at about 80 psi the motor tries to start but kicks our circuit breaker? Any help would be greatly appreciated!

Most likely it is the unloader valve. This is inline with the air filltube from compressor to tank. Somestimes the unloader valve is screwed into the tank and air tube is attached to it. This device takes the pressure out of the tube so the compressor can start without the back pressure from in the tank. Other possibility, the start capacitors of the motor. The capacitors must give a kickstart upon startup or the motor will just hum for a couple seconds and overload the breaker. A tempoary solution is to turn off the power to compressor when it reaches 120psi, then allow the pressure to drop to 40 or less, then turn power on and mostlikey compressor will start with a load of 40psi or less. It is a nuisance but it works until you replace the bad part. Goodluck,Macgivor