de restricting these engines are not easy hondas are machined with smaller venturi carbs ,valves and exhaust opening up the inlet and exhaustwill cause poor mixture and weak running best option as far as i know use top end from a early 80s cg 125 with carb or an xl125 or xl185 if you can find one without a mashed cam should fit bottom end as this engine design has been around since the 70s if your really lucky an xr200 engine will fit but thy are are rare as hens teeth good luck