Yeah, you are having the same issue I always had with cold driveability, I did get mine to be ok to be driven with the carb, however, it wasn't very responsive. Ultimately, smaller carbs have better driveability than larger ones so the 850 is probably hurting it. Of course, you don't have an exhaust crossover to warm the carb up either so that is a major hurt to it. This is exactly why I did the EFI swap. Now I can drive the exact same engine pretty much immediately.
I'll bet your stalling was either too high or two low of a float. If it's too high it may flood out and then be hard to start as well.