My SuperTigre .40 was a Jim Dandy and any brand can let a bad one slip through. Waldo is right about the needle valve probably being OK if it will run with the tank elevated. Fuel foaming is a possibility but would only show up with the tank partially full. If the leaning problem is there with a full tank, I think that would eleminate foaming problems. Is the needle valve a good snug fit in the housing? Is the 0-ring OK? If there was a pin hole somewhere in the fuel line, like Waldo says, elevating the tank would over-ride the pinhole leak and the engine would run normal. If you haven't already, it might pay to try new fuel line all the way from the tank to the carb. Some of the folks here at RCU live and breathe SuperTigres. You might post your problems as a new thread in the "glow engine" forum and you should be swamped with help. Good luck with it dutch. I wouldn't send it back until I had run it on a test stand. This would eliminate any problems caused by airframe vibration. If it runs good with the tank elevated above the model, I'd say there's probably nothing wrong with the engine.