Yes, otherwise the combustion is too hot. This can cause the valves to burn and also produces unnecessary nitrogen oxides.

Not all leanburn systems are the same. The early 2 pickup and 2 plug systems that were on 4 barrel cars were problematic. But the single pickup and single connector units that were on 318s and 360 2 barrel engines plus slant sizes were actively fine. Me and a friend have several early 80s Chryslers with 318s and they still have original leanburns.