72 overcharging

Last night I tried a battery from car that hasn't been used much recently......measured at 12.4 V. Starting up it read between 14.7 and 14.9 right off, but by the time the choke opened up, there it was jumping up over 15 V again. I just bought a new multi-meter and I have an adjustable VR on order. I also know of a vintage OEM VR that I can pull off a parts truck.