Bob, I'm using an MSD-6 with the retard as well for my nitrous. Let me look at my directions tomorrow and get back to you on this. It sounds like you have the retard box connected correctly with the yellow wire going to the white wire on the MSD6. Is the violet wire going to a 12V source that is only activated when the starter solenoid is activated? I have mine wired right off of the solenoid.
Could it be you do not have enough initial timing to start with? That violet wire will pull 20 degrees of timing out of it when activated, and if you only have 10 or 15 initial, that could be why it isn't starting.
I have the mechanical advance in my HEI locked out, and have it set at 36 degrees. The retard box drops that back to 16 degrees for starting.
