I replaced the gear ring that is under my flywheel and the gear on my starter. After I was done replacing both of them my lawn mower started right up, but it would not go to full speed. I thought maybe the carb. Needed some adjusting so I started to adjust it. Now it backfires, will not run fast like it use too. The engine is a Briggs and Stratton 14.5. If you can help me I would really appreciate it.

Hi,
I would say that in reinstalling the flywheel, sufficient torque was not applied and the key is partially sheared. They will often run, just badly; the newer, the more likely.
Peace,
Clarke