That's the problem. Sounds like the choke isn't closed/closed enough when "cold". I disconnected the choke on my /6 for the opposite reason. Mine would start and idle fine when cold but drive for 20 min then let it sit for 15 and try to start it....choke would be closed even if it were 80* out.
Engine temp forecast :) for the sake of this conversation
at temp = thermostat opens (160,180,185,190)
warm = 125 - 160*
cold < 125*
Took me a while to figure out that the choke would be cool enough to close at over 100* (bad choke stove thermostat)
