Chainsaw Repair

take the pump off and soak it in some kerosene for a few days. the check valves are gummed up. and you can't take them out for service.
another thing to try is in a container big enough, submerse the pump housing with the piston/spring instaled and tap the piston in/out very fast and firm. unscrew the limiting screw to add some more stroke to the piston. gawd sounds dirtay
you'll notice when the little check valves come loose. lift it out of the kerosene (or diesel) and give the piston a few pumps. you should see the level in the intake port go down. and the output port go up. keep doing this for a while, then switch over to a light oil. should clear the oiler out so it works again.