tazzzz

Should the OS engines run a little more rich when flying in cold weather . OS 61,,etc. and 4 strokes.? 20 -35 degrees, and what about hot semi humid temps.

Thx guys TAZZZZ[:-]

FallDownGoBoom

My Feedback: (1)

I think the prevailing wisdom is to run the engines slightly richer in cold weather. The theory behind this is that colder air is denser than warm, so for each combustion cycle more oxygen is ingested into the engine, so there's more fuel needed to preserve the correct fuel/air ratio.

As for hot, semi-humid temps, no real idea. I think I'd tune for normal operation, then set things 1 or 2 clicks rich and see what happens. You may not get optimum performance, but you can always lean things out a little and experiment.

kenh3497

Yes, richer in cold temps and leaner in warm. It does sound bass ackwards but falldown has it right about air density.

Ken

JohnBuckner

My Feedback: (1)

Yup FalldowngoBoom is correct as noted. When there is high moisture content in the atmosphere This moisture displaces the air avialible for combustion which also causes leaning of the mixture so high moisture also requires enrichening the mixture a bit (opening the main needle a bit).

John

Warbird40

My Feedback: (24)

+1.....I usually richen when cold and lean when warm

da Rock

Just setting the needle by sound or tachometer will have you turning it in the correct direction. Don't worry about the theory, just set it like you should every time you are out to fly.

Richen it up until it definitely sounds rich. (to insure you're starting from a safe setting, no other reason)

Turn the needle in until it reaches it's highest rpm. How do you know? It'll be increasing rpm from that safe setting until it starts to sag from being too lean. Just before the sag was the max rpm setting. Bring the needle back to that position.

Now back off about 3-4 clicks and test fly. Study how it flies at that setting. That setting is within a couple of clicks of perfect for that day, that temperature and that humidity.

BTW, if you're running a 4-cycle, use a tach. They're harder to hear and have less rpm range.

Gray Beard

My Feedback: (-1)

From summer, 105+ degrees to winter, 25 degrees my engines high end is usually about 4 extra clicks open. The lows temps doesn't seem to effect the low end enough to worry about.