On no account try and fix it on your own, you need a special tool. Go to any bike shop on a Saturday morning tell them you have a puncture and ask for a long weight. They should be able to help. If not try a busier bike shop.
@Ramon started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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On no account try and fix it on your own, you need a special tool. Go to any bike shop on a Saturday morning tell them you have a puncture and ask for a long weight. They should be able to help. If not try a busier bike shop.