Thanks guys. I took the valve cover off and tried prying the valve back to closed just like the first time this happened. It is stuck solid. I suspect the valve is bent which happened last time as well. I didn't try any lube on the valve as I was able to pry fairly hard and it didn't move. I don't think seafoam or oil in the gas will help since it does not run at all, wouldn't get the lube to the problem. It has fresh fuel in the tank right now. Was filled less than 2 weeks ago. Last time there was no carbon on the stem, it had gum like one would find in a carb that had been sitting. I already ordered a valve replacement kit so will go into it soon. I'll let you know if it is gummed up again.
In the future I may run some amount of Marvel Mystery oil or equivalent in the tank, but I shouldn't have to do that if the engine is engineered correctly. I'm wondering if this is a chronic problem with Generac.