I have the same engine in a Swallow ex90 mounted inverted with no real problems, and no onboard glow. My fuel tank is over the COG (back quite a ways) so I have a Perry pump to help out. I have tried to run OS engines inverted with NO success.

Where is you fuel tank? How far away is it? How high is it in relation to your engine? Check for fuel line leaks and connections.

Soooooo many factors!!!