Small Engines (Lawn Mowers, etc.): overcharging, voltage regulater, battery voltage

Question
I have a 18hp b&s engine on a troybuilt chipper. It recently started over charging the battery (voltage keeps on climbing)and boiling acid out of the battery. Is there a voltage regulater and if so where would it be located?

Answer
Wayne,sorry for the delay....had major issues linking up  so//// depending the type of alternator. If the battery is on a chipper and had vibrations for a long period of time, the plates inside may be shorted...caausing high resistance and overcharged the battery. I have to know what color/kind of wires are comming from the engine. With the engine running between 3200 and 3600 RPM's there should be approx 13 volts going into the battery max