Its because the compressor is not unloading { going above 120psi} you need to check the air signal going to the unloader valve located on top of the screw, it should start putting out air at about 90psi to close the unloader. another thing is if you are getting oil in the air coming out of the front ball valve the seperator element is bad thats the filter inside the tank the pop off valave is mounted. you can check the air signal by fethering ball valve to run the machine at 90 psi the diconnect small air line on unloade to check for air signal coming from regulater