I bought a used Asp 61 at a local auction and I'm putting it on a 4 Star 60. It starts real easy but when I throttle down it takes several seconds to slow down. On the side where the cable is attached there is a 2nd needle valve. Is this a low speed adjustment? Also on the top ther is a screw with a spring under it. What is this for? I have some instructions from Just Engines but no picture that tells me what screw to turn. Thanks