I have a Yardman YM26CS weed eater that was always difficult to start from new and became harder and harder to start over the last year or so and eventually, once finally started, would not run unless the choke was full on. Turning off the choke, even just slightly, or trying to feed any throttle in caused the engine to immediately stall. I reasoned there was a fuel supply problem. I disassembled the carburetor several times but could not find any plugged passages or other obvious problems. Pumping the priming bulb seemed to pressurize the fuel tank and delivered plenty of fuel squirting out the main line to the carb (when disconnected), so I know the gas supply was good.
Out of frustration I ordered and installed a replacement carburetor and now the unit starts easily (better than when new) and runs well. What was wrong with the old carb? These things are so simple I can't figure out what the failure was.