Hi GINMF,
The broken pipe reduced back pressure and the engine may have leaned out a little as a result. Readjust your high speed needle. Lean it out until it peaks and then back it off a feww hundred rpm. It will get leaner after it unloads in the air. Fryed engines can be caused when the engine runs too lean with no back pressure. Get a nice aluminum muffler from B&B Specialites, Ken Lambert or Wackerengines.com. It will be quiter and produce good power.

Dave