1990 GSXR 250

While riding the bike, it just lost power and died. Battery was dead. Charged the battery, bike started. Everytime I rode the bike, it would lose power and shut down. Battery at 12V when charged, draw power down to 8V while turning over and coming back to 10V. Repladed battery, same issues. Checked stator, 3 amps across all windings. I assumed regulator rectifier, swapped it out. Still have the same issues, so what else could it be?