I have rebuilt my MC, cleaned it up....and yes, I have cleaned that little hole where the returning fluid comes through. It is very small though, I could not find anything this small to poke through....and I am doing my carburetor a la Larry's instruction. When I hit the hole with the carb spray nozzle, I could see fine mist coming out the other side. In my world that means "clean passage". Anyways, when put all together the piston doesn't retract. First, I thought it is the piston causing trouble. So I pumped it out as far as I could without popping it out and cleaned it. Then was going to to push it back in with a C-Clamp and it wouldn't move. When I opened the bleeder nipple, it would slide back in. If I had not just cleaned that return hole in the MC I would have guessed to be the problem. Does anybody have an idea what it could be?