I've actually had engines idling for 5 minutes or more on the flight line, waiting for traffic to clear.

Here's how to set the low speed mixture:

1. Find the lowest reliable idle the engine will maintain.
2. Let it run for 10 seconds, then jam the throttle to full.
3. If the engine gurgles/sputters, and smokes a lot, shut down and turn the low speed needle clockwise 1/8 of a turn. Go back to step 1.
4. If the engine sags or completely stops, turn the low speed needle counterclockwise 1/8 of a turn. Go back to step 1.
5. If the engine transitions smoothly, re-tune the main needle valve, and go flying!

An major indication of the engine being too rich is that the RPMs drop when you remove the glow ignitor after starting.

Typically, the low speed mixture setting on OS .46FX engines is 1/2 to one full turn too rich.