First of all, I am not an expert in this field but have worked on several through the years. My guess, is that the float is stuck with "gook" as might be some neighboring componets. I would take the carb apart and clean each and every part (especially the float area) with carb cleaner, then put it back together and see if that solves the issue.
In the future, do continue to let it run out of gas when you store it, but use something like "Stabil" in your gas for those smaller engines that only are used sporatically. I also highly recommend a step up in the grade of gas you use in those smaller engines. Not regular, but a mid-grade usually is suggested for peak operation.