18hp Honda Idle Speed?

I have an older 44" Fastrak model # 926519 with the 18hp Honda engine. Does anyone know what the approx. idle speed in RPM's should be (both low and high end)?? I was having an idle issue that was remedied with a new air filter, fuel filter, and spark plugs but in the process I tinkered with the top exposed screw inside the air breather housing. That screw seems to adjust idle so I need to adjust it back to proper specs.



Thanks!