Hey Mike, Sounds like a problem I was having with my Avistar with an LA 40. Mine would start fine and when I throttled up it would cut out and run erratic. It sounds like you have an air leak somewhere. Check the back plate on the back of the engine. The screws could have come loose. If they are phillips type like mine had you may want to replace them with allen head type and locktite them. Also check your fuel tank clunk to make sure it isn't binding and can swing up and down all the way. Check your fuel tank plug or stopper that the fuel lines come through and make sure it is not sucking air in there. Lastly, check the fuel line in the tank that the clunk is attached to and make sure it is in good condition and not split. They fuel line in some of the tanks is pretty cheap and can break easily and you'll be sucking air in through there. That happened with mine. I installed the fuel line that came with the tank and it cracked in a short time. I could start the engine and hold the plane up and see tons of bubbles coming up though the fuel line. When I took the tank apart I found the fuel line split right where it connected to the tubing. Good luck. Let us know what you come up with.