The higher RPM in the "no load" situation tends to lean out the mixture. It may be adjusted for a perfect slow speed idle, but sneeze and stop when shifted into neutral. An 1/8 turn to the rich on the idle adjustment will keep it from sneezing, but may result in a less than perfect idle in gear. Outboards are built on compromises. Cheap – Dependable – Fast – pick any two . . . 😆
