360 running on 4 cylinders

One thing that changes as the engine gets up to running temperature is valve lash (clearances). The carb settings don't change?? The intake doesn't change unless it's developing a leak (on one side) when it gets warmed up from heat expansion?? If the problem gets worse as the engine gets up to running temperature doesn't the problem have to be related to engine temperature rise??
Exhaust heat riser??