Welcome, sorry to hear of your issues. Valves are simple enough to check, I would start there. Once that is ruled out, there is a 99.99% chance that the carbs are still the issue
These little ninjettes have the most finicky modern carbs I have ever dealt with, and they have to be kept
beyond clean to work. I finally wound up sending my set off to fellow forum member ducatiman who offers quick and reasonable refurbishing services. Now I just run Sta-bil in my gas and give them a quick blow-through with carb cleaner and compressed air after I pull the bike out and it's good to go!