i have a craftsman 16" chairsaw, used once about 20 years ago. now, i can not start the engine. put couple drops of gas right in the carburetor, it fires. but it would not suck fuel from the tank. the fuel filter in the tank looked clean. took two plates off the carburetor, it seems that (fuel pump and metering) diaphragms are all in good condition. what is wrong and where should i start? thanks.