I have checked all of the lines and they hold pressure.... Could it be an air leak at the front bearing? The fuel tank pickup seems to be working normal and moves as should when inverted, etc... Yesterday, I did a sharp turn and the engine sputtered but kept running when I backed off the throttle.... Then I did a loop and the engine quit... next flight I did another loop and the engine sputtered again but kept running... Tryed it again in the next flight and the engine quit in a tight loop.. This has never happen with this engine before so I am baffled.... it is an Enya 60 two stroke...each flight I added a few clicks of rich and it is smoking normal... Held the airplane straight up each time before take off and it takes full throttle with no problem... seems to run good held straight up and during the flight except as noted....