I have a Super Tiger .61 that I have had for several years. I just put it on a new plane. After tuning the engine on the ground it seemed to run great. The problem comes when I pick the airplane up and hold it in a vertical position (or upside down); it dies. If I quickly lower the airplane to a level position it will regain itself and continue to run just fine. I have tuned and retuned everything I can think of to no avail.

Any ideas? Do you all think this is an engine problem, or a fuel problem? Please help. Thank you all in advance.