I have a 12 hp. Briggs & stratton on a craftsman riding lawn mower, and the gas is getting into the oil, every time I check the oil, I get more gas on the dipstick than oil, does anybody have any suggestions on what I may be able to do to fix this problem, or what will cause this, and how to adjust?

You could have a microscopic piece of debris hanging the needle valve open allowing the carb to flood, then the fuel goes into the intake, seeps past the valve and rings then into the sump pan. You may want to remove the carb and clean it. Then replace the fuel filter, and drain and clean the fuel tank. Then you may want to invest in an inline fuel line shutoff valve. The valve if used will prevent this.