Tuesday go out and fly  FP 25 apc 9x4 hayes 3 ounce tank  28 ounce magician  2 flip start run up to 12,500 back off to 11,900 os 2030 muffler
20 % oil 1/2 n 1/2  10 % n
perfect run steady all the way thru  2nd flight runs half way thru tank and quits
Check for leaks non check to see if needle came loose none  Plug was tight and looked good
today fire it up first flip  run to 12.5  and back off to 11.9 perfect run ----- hour later try again   quits with half a tank
YuK
Fred Q

     Hi again Fred:
     I got a vibe that your problem may be heat related.  You first, good, flight is the first one of the day in both examples. The second, bad flight is after the plane has been sitting in that very hot sun for an hour!  What else had changed, NOTHING! Try keeping our plane out of the sun and in a cool place.  Perhaps the fuel is also becoming too hot and thin leading to a lean running condition.  Thermal runaway?

             The above is just a guess.  I have seen that combination run very well in cooler weather.  The only thing that has changed is the ambient temperature.  You did not fly it the other day when the temps were in the 90’s!  The last time that I saw it fly was when the temps were 75-82 degrees.  It few great that day! 
Something to               
               

                                                                                      Good luck,

                                                                                      Frank

     Hi again Fred:
     I got a vibe that your problem may be heat related.  You first, good, flight is the first one of the day in both examples. The second, bad flight is after the plane has been sitting in that very hot sun for an hour!  What else had changed, NOTHING! Try keeping our plane out of the sun and in a cool place.  Perhaps the fuel is also becoming too hot and thin leading to a lean running condition.  Thermal runaway?

             The above is just a guess.  I have seen that combination run very well in cooler weather.  The only thing that has changed is the ambient temperature.  You did not fly it the other day when the temps were in the 90’s!  The last time that I saw it fly was when the temps were 75-82 degrees.  It few great that day! 
Something to               
               

                                                                                      Good luck,

                                                                                      Frank

The bold is the only change I made to your post, Frank! Thinner oil would cause rich running, not lean running as you stated.

I've experienced the need to lean the engine from early AM to mid-afternoon flights, in order to get the same launch RPM. I'm not convinced that it is entirely due to reduced viscosity of the fuel, but maybe. Perhaps somebody will try keeping their fuel at a constant temperature (somehow?) and report back? I am a devotee of getting the engine warmed up before setting the NV with a tachometer. Some don't, and don't change the NV from flight to flight, but sometimes they have problems that I don't!  Steve