Small Engines (Lawn Mowers, etc.): RPM, torque converter, converter system

Question
I have tecumseh ohh60 6hp engine that i need to set the rpm i noticed that there is a screw at the bottom of the bowl that when i unscrew it it starts and runs but i screw it in and it troubles starting, runs but doesn't accelerate it has a torque converter system that only engages when the rpm is proper iam guessing screw does the trick, any help?

Answer
Jose

The screw on the bottom is the main jet,leave that in the position you found it. That is not the way to adjust the rpm's I need the rest of the engine numbers for me to help you further,the equipment you are running with this should have the correct RPM'S needed to run this.