It's not the check valve. The check valve just ensures you hold pressure in the tank.

Since you have pressure in the tank fuel wants to flow through the carb unless your regulator stops it when not running. Something is wrong with the regulator... Probably need to send to YS.

By the way, you will be very happy with the ys.63 ... It's just outstanding - reliable, predictable, and powerful.

Sorry to hear about your misfortune.

Mike