Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Sound s like the charging system is not charging the battery and the battery discharges while running, or after you turn the unit off. Do you have a voltmeter to test battery voltage? Is battery above 12.5 volts? A new, fully charged battery will be over 13 volts.
Usually the voltage regulator, but it can be the stator /charging coil under the flywheel.