Disconnect the old 6 volt battery first and then just hook up the 12 volt, as frenzix says they love it. Dont turn it over for to long, the engine loves it, but the starter hates it, something about the speed equation and doubling the voltage thing. You can damage your good battery if you dont disconnect the old one. Run it 12v for a while wont really hurt the genny the regulator will have a few kittens and click away like mad but the the 12 volt battery will drain a bit quicker than normal.
As I do this as job, I will put in myn 20 cents worth. Its not a problem, just dont leave it connected to long or have anything in car turned on, radio, lights etc, they might not like. Its always a good idea to keep sparks away from batteries, they give off highly explosive gases. So the best way to do it is, connect both + & - at your 6 volt car, connect the + to the 12 volt car, then connect the - to the 12 volt car somewhere on its block (the engine lift points are good for this) as you start the 6 volt car, once the 6 volter is going remove the - on the 12 volt car 1st.
hey sam if you are wanting to make life easier. get yourself a battery isolator and a 12v battery fitted. wire it to the 6v then each time you want to start it you can jsut flick the isolator to the open kick start the car and then close the isolator. worked for me for my old 6v's. just dont forget to close it. i had the switch sitting jsut behind my seat so i could have one hand on that while turning the key.
Seriously though, if your battery is dead flat (or even if you don't have one, make sure +ve terminal end is insulated from body) you can use a torch battery. (the big squareish ones, like in eveready dolphin torches are best as they are 6v but combining smaller ones to total of 6v will do). Wire +ve straight to the coil +ve and -ve to a good earth then clutch start the car. Higher gears work best (3rd or 4th) but you have to be quick to disengage clutch or it will stall. Disconnect torch battery as soon as car starts. If your car has a generator you can drive around without a battery as long as +ve terminal end is insulated from body. Do not start or drive without a battery if you have an alternater as you will wreck it (blows the diodes)
If clutch starting is a problem because of lack of room (parked in garage etc.) you can easily start a dub like a lawn mower. (or any car as long as it doesn't have a limited slip diff). Just chock the front wheels so car won't move and fall off jack.Then jack DRIVER SIDE rear wheel until it's off the ground, then wrap a length of rope around the tyre in a clockwise direction and with car in top gear and ignition in the "on" position, wallk briskly away from the rear of the car pulling the rope with you as you go. (if you need to use passenger side wheel then you must wrap rope anti-clockwise)
Works every time, as long as engine is in a reasonable state of tune. You wont get injured by rope if engine starts before you're finished pulling as direction of wheel rotation throws the rope off the tyre anyway.
DO NOT EVER TRY THIS ON A CAR WITH A LIMITED SLIP DIFF AS IT WOULD BE VERY VERY DANGEROUS.
