Yeah, same for me.

I just cut a bit of cardboard to fit, covered it in gaffa tape and stuck it in as a temporary fix.

I know others have made them out of plastic box lids and so on.

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Bike: 2013 XT660Z, TKC70 tyres

Mods:
Barkbusters, Scottoiler, DIY Tail Mod, DNA Stage 3, Power Commander V & O2 Eliminator, Exan X-Black Stainless exhaust, Tool tube, Ohlins linear front fork springs, Nitron rear shock, JT front and Supersprox rear sprockets, D.I.D. VX 520 chain, Adventure Spec bashplate, DIY USB Outlet, DIY chain guide, Kev's Throttle mod

http://www.facebook.com/onemooseonemotorbike