Dave I am having problems with a new YS91. So far it has about 18 ounces through it in a rich break-in (2 turns out) ground run. I have a APC 15x8 prop using Powermaster 20/20 fuel with an OS type F plug. I am using a 14-ounce tank that the lines come out on the carb centerline. The engine is horizontally mounted with the muffler side down. I have a two-tee fuel setup both behind the fuel filters and check valve. The check valve is setup so you can blow back into the tank. The check valve is on the vent side and I am using a filter on each line going to the engine. The problem is fuel is leaking out of the carb when you shut it down at a rate of 2-3 drops a second until I relieve the vent pressure. The regulator is set with the brass screw flush with the bottom of the casting. Any ideas? OK here is where it gets weird. My wife’s uncle is also trying to break-in a YS91 also and he is having the same problem. These are brand new engines. He is using a 3-line set-up with the one plugged. Hard to believe that two engines have a problem so I guess it is in our set-up but I can’t see what is wrong.