12v start on 6v system

About a starter turning over good on 6V and not dragging, I suspect the starter is not the problem. Something to consider is the newness of your mill. If it's still a little
tight, it takes a lot of voltage to crank it over when hot and clearances are minimal. After a 1000 miles or so, it'll be loosened up and may start up when hot. If the trouble persists, try this to determine where the problem is.... get the engine hot and shut it off. While your waiting for it to heat soak and get hard to start, connect
one post from a spare 12V battery directly to the starter post (you don't need to remove the 6V cable). After you're sure it's been long enough and the engine is hard to
start, connect the other post of the 12V battery to a ground on the car. This will engage the starter using 12V. Then, the 6V is dedicated to only the ignition system. DO
NOT PUSH ON THE 6V STARTER BUTTON WHILE THE 12V IS ENGAGED! If the engine fires right up, you know the starter is pulling too much load from the
6V system and there isn't enough left to fire the ignition properly. These flatheads sometimes get balky when shut down and especially if they're built up with more
cubes and compression. Mine does. So I run both a 6V and 12V battery. Everything runs on 6V including the starter. The 12V is also connected to the starter and has it's own starter button up
under the dash. If it won't start right up with the 6V, I stop using the 6V button and hit the 12V and it fires right off. The 12V battery doesn't charge from the car's 6V
generating system, but is a total loss system. I trickle charge it overnight only twice a year since it doesn't take much to start these engines. Write me if you want to know how to hook up both batteries.