Another thing to look at is your pickup line in the fuel tank. If it doesn't move freely in the tank, is stuck at the bottom of the tank because the fuel line is too long, then when the plane inverts the clunk will no longer be in the fuel and the engine will die. This would explain why simple rolls or loops it doesn't die, because there is enough fuel in the line for you to come back upright and the pickup can now get fuel, but when you invert it dies.

Hope this helps

Ken