Hyfax is the plastic strips on bottom of the slide rails in the rear suspension, without them you would be running aluminum rails on steel clips and the whole works would wear out in a short period of time. These plastic strips, hyfax, slide over the rails and are held on by 1 bolt or rivet at the very front, they are designed to take the wear, and fairly cheap to replace when worn out.
Now as far as your popping, it sounds like you have it narrowed down to the engine, I guess the first thing I would do is reset your track tension, loosen it up some, and pull the carbs off and clen them real well, then see how it goes.