The Holley tuning guide tells us not to change more than 4 jet sizes from original. If you need to change more than that, change the CFM of your carburator of choice. IMO 850 is too big, but that is probably not your starting problem. Even an 850 should start without the WOT if it is not leaking somewhere into the intake. We have to remember that the CFM rating is WOT, and that is the amount of air it will flow. The necessary fuel for the 850 CF of air will vary with conditions, but I don't think hard starting is related to the size of the carb, and I doubt the main jets are flowing while cranking to start. Sounds like high floats, or leaky needle seat assemblies.......MP