Chainsaw Repair

I have 3 of these carbs that are bad. Tim or killiansredleo got me in touch with a gentleman selling them new for $50. All the bad ones would tune out & sound ok but after WOT rpm drop would not idle & just die. The new one worked fine so I pressed out the little valves from the good & into the bad using a bit upside down in my drill press & all was good so the problem lies in those little valves.  I tried to order just this part & zama had quit selling just the valves. What makes them go bad, I don't know, big possibility that it's a bad fuel issue.