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.

Your carb my be leaking around the crankcase. Maybe the oring cracked or dried out.

I don't know the answer but (this is just a thought) can the baring be out of lube ot broken. That might be the rpm problem but im not sure

i think Insanemoondoggie is right on.i had the same problem with the same engine it was the carb o ring.when you tighten the carb hold down pressure on it.

In addition check the the backplate is still tight and check the bleeder hole on the front of the carb is clear.

You can do this by opening the mid range screw several turns an then pushing a thin pin all the way through. Then close the screw back in untill you can feel it on the sloppy fit pin.

John

Well I check those things and everything seemed ok. The gaskets looked good but I'm going to get new ones just for the sake they're so old. We'll see what happens. Thanks for the info. Not sure waht to do if this doesn't work though.

Where can you get gaskets and o-rings for O.S. engines (discontinued)? Thanks

You can get them online at Tower hobbies. They carried my out of producttion gaskets there but I was lucky enough to have my local shop have them in stock.

So, I switched out all the gaskets and it seems to be running very well. The true test is when I can get it up flying because it tended to act up in the air. We shall see. I thank you for all the help and hopefully we have fixed the problem!