Tight spot on the chainring, misaligned rear cog, something like that . . . .
If you've done the other obvious things (front wheel spins ok and doesn't rub on brake if you have one) then I'd imagine it's one of the above
@Ste_S 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.
If you've done the other obvious things (front wheel spins ok and doesn't rub on brake if you have one) then I'd imagine it's one of the above