I have an MDS.61 that will start,tune the high end, then dropping back to idle will not advance beyond 1/4 throttle.No amount of needle tweaking helps. I have even tried an on-board Glo-driver.The engine hand starts easily and has the best idle I have ever seen.When you can get full power it cetainly has plenty of grunt. So excellent idle or plenty of go, just not both at the same time.Would changing carby help? Or should I take a sledge hammer to it? I also have a MDS .25 I bought for $50 brand new. It is a little gem and I have no complaints with it. Can someone save MDS's tarnished reputation? My other question is this: Since 4strokes cost double the price of equivalent 2 strokes , what are their advantages? Specifically I.. I am debating between a Magnum XL- FS 120AR Four stroke.a Super Tiger G90 and an O.S 120 Ax. I have also seen an ASP 1.20 Four stroke advertised very cheaply but I have never heard anything about these engines.Any advice will be greatly appreciated. P.S . The engine is to power a 71 inch span P-51B from the David Vaughan plan