hi, my 25hp evinrude idles fast so as when i am trolling boat moves to fast.i tried adjusting screw on linkage that lets me turn motor handle to lower speed.when i do this motor idles slower but after about a minute motor starts to idle rough and stops.a friend of mine told me to turn carburator screws in a bit and try readjusting linkage screw again.i am a novice at this and would not want to mess things up because apart from this motor runs excellent.would this be a good way to start to try to remedy this problem. thanks in advance.