Hose the fuck out of the shifter with GT-85 or some other grease-shifting kinda spray and see if it improves. Also - you sure cable hasn't snapped in the shifter? That's where they usually break. Have a look for frayed wires.
@hippy started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Hose the fuck out of the shifter with GT-85 or some other grease-shifting kinda spray and see if it improves. Also - you sure cable hasn't snapped in the shifter? That's where they usually break. Have a look for frayed wires.