I wrap the fuel tank to the base with rubber bands and run a music wire throttle control rod through the rubber bands.  Keeps enough friction & tension on to hold settings and is cheap, infinately adjustable and easy.  My "test stands" are 1" x 4" x 18" +/- planks with a cut-out for the engine.  I clamp them to a sawhorse or the lower deck (I learned to keep oil & fuel off the deck proper or THE ADMIRAL gets testy).  For gas I bolt a piece of 2" x 6" to a vertical deck post.