I had an APC prop (on a OS40) that was out of balance.............vibration was severe enough that it caused bubbling in the fuel tank and lines. This was not a problem at high RPM....but at idle, the engine would run fine for a few seconds and then collect one of those air bubbles and die. Tank and all fuel lines (internal and external) were inspected 2 or 3 times. No holes or leaks.............a more experienced member suggested checking the prop balance.......put on a balanced prop and have not had a problem since.