if what bb said doesnt help it then go for the reed valve,its common for these to crack or get damaged and this is a symtom of this.its under the inlet manifold that the carb is screwed to.you will need to take the seat bucket out to get to it,i did one about a week ago funnily enough.
adam bike doctor
March 2010
water in petrol or blocked jets. clean carb out and make sure all jets and clear. Pop a new plug in it while your at it
bb
March 2010
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