If he has a 6 volt flywheel on the engine, won't he have to change it out to use a 12 volt starter?
Could the 6 volt solenoid be changed to 12 volt or are their sizes different as well?
If he's using a stomp starter then it should last a long time. But if 6 volt solenoid on 12 volts won't last but a few minutes at best.