it isn't enough of a restriction to matter. there is something else wrong if the engine can't stay at around 210* under all conditions. how old is the radiator? water pump? do you have an intact fan shroud for the mech fan?
items that can cause a sudden rich situation include: bad coolant temp sensor, bad O2 sensor, or an injector that has failed in some manner and is spewing gas in an uncontrolled manner.