This seems to be a sorta common problem. I've had it a few months and got around to replacing the canister valve, with no luck. Better weather has come and don't have a garage,here's what I tried and couldn't believe it worked. The lines coming out of the canister are what you are after. The fattest line had charcoal stuck in it, causing a clog. I used a shop vac and sucked it out, then blew it out to make sure with the vac. The fat line I think goes from the fuel pump to the canister, the fuel pump side is hard to get off, I just loosen it to get a better flow. This can all be done through the opening for the fuel pump. Just don't know how the charcoal made it out of the canister to the line.
It's an easy fix and might help some of us with the problem, cause I tried everything that has been posted here with no luck.