Hey rcign I have a ? for you. My zdz 40 does lean out on the low neddle as the tank emptys. I adjust the carb at half tank, as instructed.After filling the tank the motor richens a bit, if I lean it back out a bit it runs great untill half tank. Then the throttle won't respond smoothly, almost cuts off. Land the plane , richen the neddle 1/8 to a 1/4 , everthing is fine again. The engine has a bing carb on it now. ZDZ has replaced it with a walbro carb but I have not installed it yet. Engine run well ,has 5 gals of fuel thru it. The fuel tank is 6 in from the carb and has been inspected for any air leaks. Thanks Kent