That has an Impco regulator, right? Sounds like there may be low vaccum. Maybe check for a vacuum leak. The regulator and the lock valve need good vacuum to operate properly or it could be any of the fuel system items being dirty or needing replacement because they are not allowing the fuel to turn on or flow when cold starting. Try "choking" the carb with your hand instead of shooting propane in there, when cold, and see if that makes it start.