monkey, you won't have any issues with a 6V stomp starter on 12V, with a key start [from a 6V car] there will be a solenoid that isn't on the foot starter, and it is not likely to take 12V
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics