dristo72,
It sounds like the valves are not seating correctly.
The steps that I would take first are:
1. Remove the muffler
2. Remove the valve cover (two screws)
3. Check to see if you have valve clearance.
4. Remove cylinder head.
5. Remove valves.
6. Check valve seats.
7. Reface valves & Seats.
8. Reassemble & reset valve clearance.
Check this first and let me know what you find.
The workshop manual is quite large for the Briggs & Stratton motors and it will take some time before I can upload it to the board.
If you have a look at posts you will find a link to parts manuals that I have put up on oner of the recent posts. That will give you some idea of assembly etc.