I'm pretty sure that it isn't tank oriented. The vent line is definitely clear and functioning properly. After it gets warm and starts acting up, it draws air in at the carb and lets the fuel siphon back into the tank. It acts as if something is warping once it is warm allowing air in. With the exception of the front seal, the plastic back case and the joint where the carb screw on are the only two places to draw air. I'm pretty sure it isn't the back plate because it is well gasketed and has the aluminum mounting plate that fully covers and compresses the plastic plate to the aluminum case. I'm guessing that is is either in the carb or at the joint where it screws on. Why would it run like the proverbial striped *** ape for 12 or so minutes before acting up and when allowed to cool down, run well again repeating the whole process? Thanks guys, Todd