Hi guys.The Muffler assembly that is fitted to the DHZ and a few other bikes is able to be de-restricted fairly easily.Remove the pop rivets front and rear on the muffler can,remove the core assembly.cut the 2 plates off the perforated core and keep them.We throw out the STD factory perforated core and then roll a new 30mm perforated core using 50/50% 4mm Dia hole sheet.Look up a 2 stroke pipe maker in the ph book they can make you a 200mm long core for under $20 [or pm me]..Now re-assemble the core and end plates and trial fit the whole lot together.It is trial and error cutting/shortening the perforated core until the whole lot is a nice tight fit with the alloy muffler end caps.Grab the MIG or oxy weld the inner core and plates together.Re-asemble again fitting the Pop rivets this time,Bolt her back on yer Pitty,kick her over crack the throttle WFO and drive your neighbours dogs crazy !!!!.