Idling speed For mariner 40hp

[PatrickMonahan]

What would be a good idling speed for my 1980s mariner 40hp 6e9, it's idling at around 750rpm and won't idle any less or it will stop

 

[DavidMoore]

800 RMP would be good, but under the following conditions:
- a warm engine
- boat in the water (not on hose / muffs)
- the engine in forward gear.