lml@lancaironline.net Mailing List Archive

An additional point - If an electronic ignition is used, it is important to properly set the idle lean mixture and it will always be leaner than the same engine using ordinary magnetos. Because idle and taxi power is so low (low rpm, low map), the spark is advanced quite a bit, sometimes to about 34 DBTDC. I have a dual Plasma III system and after an engine start I always lean the mixture and see a rise in rpm. The mixture remains leaned during taxi and run up checks (1800-1900 rpm) as this is a greater stress on ignition components - there is no engine stumbling and shutting off one of the ignitions only results in a drop of 10-20 rpm.

Grayhawk

IO 320

In a message dated 12/27/2012 8:54:40 A.M. Central Standard Time, casey.gary@yahoo.com writes:

I agree with Walter. The only problem with being a little on the lean side (as yours apparently is) is that when cold the engine might not keep running if brought back to an idle, and it may stumble if the throttle is opened abruptly from idle when cold. The problem with being rich (the 25-5-0 rpm drop is pretty rich) is that when operating at a high-elevation airport if you don't lean it aggressively at idle it can quit. Like on roll-out after landing. BTDT. Regardless, it only affects operation on the ground. If it is running good, I wouldn't bother changing it.

Gary Casey

The 25-50 RPM rise should be seen at sea level. What's your home airport elevation?

(I prefer to have it on the lean side.)

Walter Atkinson
Advanced Pilot Seminars

On Dec 26, 2012, at 6:23 AM, Greenbacks, UnLtd. wrote:

My IO360 idles smoothly at 760-780RPM.
I've been told that the correct mixture setting at idle has been achieved when pulling mixture to full lean
results in a 25-50RPM increase before the engine quits. Is this what I should be looking for?
I don't see it yet so I'm thinking I should richen up the mixture a click or two until I see the rise.
What do our resident engine experts say?

Thanks,

Angier Ames
N4ZQ