its had a seizure i expect mate the chuffing noise from the exhaust is a classic symptom of it,its the unburnt gases igniting in the exhaust.the compression must be very low for one reason or another more likeley a seizure or possibly a leaking head gasket as this is not uncommon either especially using a pattern gasket.take the exhaust off then the head then the barrel.inpect them for any scoring or other damage.dont forget there will be a reason why it has done it.
adam bike doctor
May 2010
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