Power loss, with voltage drop ?

Hello guys I have a 2012 razor 800 HO, Im running into a problem with a power loss only when voltage drops to 13.5 volts. as soon as the voltage goes back up to 14.2 volts i can have full power. So you could imagine every time the coolant fan kicks in or the light bar is on i have a power loss, the machine goes into like limp mode or something. The machine never backfires and runs great when voltage is high. I have checked grounds and battery is good. Any help would be great thanks Guys !