Knuble's first goal capped a two-goal second period. His second gave Philadelphia a 5-1 lead at the second intermission.
Carter added two assists, while Martin Biron stopped 23-of-26 shots for his third win in four starts.
It was the first time since Oct. 28 that Philadelphia scored at least six goals in regulation.
Pittsburgh's Jordan Staal, Eric Godard and Ruslan Fedotenko all scored once.
Dany Sabourin surrendered all six goals on 27 shots in the Penguins' fourth setback in their last five outings.
The Flyers went 4-for-6 on the power play, and the Penguins went 1-for-4.