Stale fuel issues

[EFSM]

261 is more lock prone than many other saws. I’m not sure where in the fuel system the problem lies, but my suspicion is the metering side or the main jet of the carb. It’s interesting you are getting zero start. Usually a vapor locked saw will struggle a bit. .

A stiff metering diaphragm is the most common reason for super finicky carburetors, in my experience. However, Zama’s black plasticky pump diaphragms can also swell and not flex as a result.