Most certainly check valves are a problem, especially with a bike that has set for a long period. The additive packages in some 2 stroke oils tend to separate and gel around fixtures and low points. (Gummy). As memory serves, some early check fittings were rebuildable, latter was not. That change occurred on DT175 twins after Oct. 1965 production. ALWAYS a good idea to check your tank filter as well, making sure it has integrity and isn't collapsed or compromised. On unknown new projects it's good to start from supply and work through to delivery points. Saves grief.
