I had the same problem with my 39 Deluxe Coupe, the best advise I received was from GM....quote "Save your money, get some 1/0 cables and it will spin like 12 volts" I did just that and my starting problems were a thing of the past.
This is in response to a hard start issue I was having on my 36.
It turns out that my pumping of the gas pedal when restarting a hot engine was flooding it preventing starting when engine was hot...I pump the throttle to start when cold but can not when hot....took me a while to figure my problem out.
Thanks to all for the suggestions.