Hello all,
My push mower is making a sputtering sound every 4-5 seconds. When it makes a sputtering sound it also puffs dark smoke. It still mows... but doesn't sound healthy. Also, I recently changed the oil and it was fine the first use. 2 weeks later it started acting up.

Details of mower:
Craftsman: Powered by Briggs & Stratton
550 Series
158cc
5.50ft-lbs gross torque per SAE J1940

Any ideas on what the problem is and/or how to fix it?
Thanks in advance,
Jake