NEED ADVISE! PLEASE

HELLO, MY NAME IS TERRY AND I RECENTLY BOUGHT A 1980 KAW KZ 750 LTD. I HAVE DONE SEVERAL THINGS TO THE BIKE, BUT I CANT FIGURE THIS ONE OUT ON MY OWN. WHEN THE BIKE IS CHARGED, IT WILL STAY RUNNING AS LONG AS YOU WANT IT TO. IT WONT RECHARGE ITSELF THO. AFTER RIDING A WHILE, WHEN I STOP AT A STORE, IT WONT START WITHOUT A JUMP. CAN SOMEONE PLEASE TELL ME THE CHEAPEST WAY TO FIX THIS?

Make sure your battery is fully charged, check the voltage with the rpm's at around 4K. The battery MUST be fully charged before you test it. It should be putting out around 14 volts or so at 4k. If not it will most likely be the regulator. If it is putting out that much it will be the battery. Also check all the connections and ground to the frame.

THANKS! I WILL CHECK THAT.