I have an Aerostar 40 that I've had for almost 15 years. I have an O.S. .40 FP that is just as old. I took about 12 years off and I've been flying it for about a year again. Since I started flying again it seems as if the first flight of the day it runs beautifly. High end great and low end great. The second and thrid flights, the engine runs and idles well on the ground. As soon as I get airborne it's as if the plane starts to run rich and blubbery. I get no RPM change from 1/2 throttle to full throttle. It just sounds cleaner at 1/2 throttle but not a ton of power. Ok it right now sounds like a high end adjustment, but here's the catch; if I go to idle on the stick, it might decrease to 4000 or so RPMs but doesn't come down. To get it to come down in RPMs I have to "rev" the throttle stick to 1/2 or full throttle to, (it seems like) clear it out, and then it will come to an appropriate idle again. It just makes flying a bit more challenging. Is this one problem, two problems, a tired engine, a rookie mistake? My O.S. .61 flies beautifully in my Venture 60 through.