I have a 17.5 hp briggs and stratton it runs rough and back fires at high rpm runs smooth at lower rpm I have adjusted the valves cleaned the carb replaced the spark plug new airfilter new fuel filter.
We can not see hear or smell you engine,
So we have no idea if you are talking about a horizontal twin , side valve single , overhead V twin or OHV single,
Runs rough is about as good to a mower mechanic as you walking into your doctor & say "I don't feel well".
Just like a computer , garbage in = garbage out.
So if you really want help full Model number then describe
1) exactly how it is running rough
2) exactly what you have done.
There is a massive difference between squirting some carb cleaner down the throat & ultrasonically cleaning a dissasembed carb.
Then a little about yourself helps as well mechanical aptitude, length of time playing with engines etc etc etc.