I can see the needs for the modifications to the 84 , but they're not necessary on the 90 . Saito incorporated the majority of the Ray English mods in the 90 at the factory . The 84 has been run successfully without the mods but it runs much better with the updated intake plenum for better fuel/air distribution . The key to a long life of both the 84 and 90 is to run 15:1 mix and keep the static rpms at or below 6000 rpm and unloaded rpms below 7200 rpm. Baffling is a must for proper cooling in a cowled engine to keep the cylinder temps below 250f max temp