Craftsman riding mower is around 7 years old. Engine, not mower, surges in idle and while mowing; replaced plug, gas line, gas filter, filled w/new gas, & air filter. What else can I do?

Two things come to mind:

1. clean governor to carb linkage and throttle plate on carb.
2. Carb problems - disassemble and clean

Yes the governor is the most likely culprit

I had the exact thing happen to my 7 yr. old 42" craftsman. Mechanic took carb apart and said the "needle" was sitting in hole properly. Took him 5 min. to take it apart, re seat pin, and put back together