Why should the IDLE MIXTURE ever need adjustment?

[DJ_Allatoona]

1986 Merc 75 HP 2-stroke. It will stall sometimes when idling, usually after the motor has been running for awhile. Example, coming back to the dock after a few hours on the lake, in the no-wake zone, I will just idle & drift....and the motor will stall. But when first starting cold it will idle forever. I leave it running to warm up while I park the truck, and get stuff ready. No problemo.

So why would it want to stall at the end of the day?

I will tinker with the idle mixture screws tomorrow, but it just made me wonder why they ever need adjustment. If they're set properly ONCE...do they vibrate out of adjustment? As the motor ages and weathers, does it need the mixture tweaked?

Sorry if this is an elementary question. I can be a big dummy.

Thanks.

 

[MTboatguy]

Wear over a period of time, vibration, elevation, humidity, temp, there is a lot of things that can cause you to have to tweek an idle mixture set up, when setting a mixture you are looking for the happy medium that will provide best run ability in changing conditions.