seeing that we have alot of specialists around could someone please help with the following

we have the engine mounted inverted with a custom build pitts exhaust on it. its brand new and still being run in. it starts very easy but for some reason if you pick up the tail wing to level the plane on the ground the revs drop, and if you shake the plane a bit the engine dies. we have tried putting it on an external tank. we have also turned the plane upside down and then the problem is worse. opened the carb and checked it out, there was a little dirt but not much to worry about, there is no air problems due to cowls as the plane is still on the ground with no cowl.

we have also leaned it and riched it out same problem

PLEASE help