My 310 starts and runs fine but then it quits. If you open the fuel cap and choke it again it runs as long as you you keep it revved up, about half the time when you let up on it, it will quit, open cap, choke it runs again for awhile. My dealer is pulling his hair out, we have replaced the vent tube and grub screws twice now. He is using Stihl tubing. Doesn't know what to do. It gets real frustrating restarting that saw a dozen times or more every tank of gas. There must be some solution? Thanks. Jim