I also have an mds .40. The way I tune mine is to give it full throttle then squeeze the gas line for a second until the plane revs up. Then I lean it out a little bit and squeeze the gas line again to see if it revs up. If it does then I lean the needle a little bit more. I do this until when I squeeze the gas line for a second it dies. Then I turn it like 2 clicks to the rich side. Works every time.