Need help with gas powered air compressor

[kd7kmp]

I have a twin tank, gas powered air compressor. The unloader valve (controls when the compressor adds air to the tank) is not adjusted correctly. It fills the tank to approx. 120 psi, then it waffles the engine throttle control up and down without ever really "turning off" to allow the engine to idle. It's really annoying.

Does anyone here know how to adjust the unloader valve on compressors like this. The compressor is a Porter-Cable CPL55GH8W 5.5-Horsepower, 8-Gallon Gas Powered unit. The instruction manual gives no help on this. Thanks.

Kevin