Replace the copper line with another, or mate in a rubber hose instead. The rich/lean knob should be attached to a high or low-speed needle that adjusts by turning clockwise or counterclockwise. You sure there's nothing attached to the knob? Photos would help. Have you checked compression, tank/fuel line/carb cleanliness, spark, lower unit lube? Those are nice little motors, very simple and reliable. You can get old Evinrude service manuals at
www.acmeoutboards.com. Post back and let us know how it goes.