A couple of reasons your problem could appear to be gone - you could have bought fuel somewhere different than your normal station and its formulation is different making it less susceptible to evaporation, or your ambient air temp since you have put in the check valve has been cooler, again preventing evaporation. No sarcasm, just stating real physics. Fuel simply cannot physically drain from the carb float bowl back to the tank,the same as your kitchen sink cannot drain through the tap. Hope your problem is gone away, good luck.
Dave
