Both mowers started doing the same thing at almost the same time this year. They will run on the left tank (the one w/ a reserve) and, after using about 1/2 a gallon of gas, I have to switch to the right tank because it won't take any more fuel from the left side. Any ideas what could be the issue or how to correct it? I haven't ever messed w/ the fuel tanks on these mowers before so I don't have a clue what's going on. 23 Kawasaki/61" deck on both mowers if it matters. ~1000 hours. New fuel filters.