Hi there:

     After many flights on a good stunt plane-engine combination, the engine has started to run very rich when inverted.  The tank is a metal Uniflow that has performed flawlessly.  Nothing in the engine has been altered.

      What changed to cause this disaster?

       Tia,

       Frank

       

       

I ran into the same thing a while back with my ST60. Engine ran fine and then one day it started to act up. I checked and replaced just about everything you can think of except one thing. 

Come to find out all I needed to do was replace the glow plug. Once I did that my ST60 purred like a kitten! 

Dennis

     Hi there:

     After many flights on a good stunt plane-engine combination, the engine has started to run very rich when inverted.  The tank is a metal Uniflow that has performed flawlessly.  Nothing in the engine has been altered.

      What changed to cause this disaster?

  Impossible to say without seeing it. The most obvious answer is that the tank is moving around, but, it's possible that the uniflow vent tube has come loose, or that the overflow tube or plug has cracked or is otherwise leaking air. Remove the tank and inspect it, wiggle all the tubes to see if any of them move, then check for leaks. Note that *all* the tubes must be soldered both where they go through the wall of the tank, and to the inside of the tank where the end, or they are guaranteed to shake loose at some point.

    Commercial tanks also typically use brass tubing rather than copper, and they will all eventually crack or erode away.

     Brett

If the tank uses brass tubing you're gonna need to re-do the tank.

If something changes , let's look at the variables. Is the temperature colder or more humid ?  Could there be an obstruction in the venturi  ? Or could there be an amount of old fuel that was in the needle valve that has finally broke down and no longer restricting the flow? Or has the glow plug gotten weaker in some way? IC engines only have a few variables but they can be odd at time.