Mixture Responses on Lycoming O-360 Fixed Pitch Prop

I am the happy new owner of a 6A with an O-360 and a Sensenich fixed-pitch prop, Plasma-2/Slick + Ellison Throttle Body Injector. (I will miss the rotax engine on my flight design ctsw, which I will have to sell now.) of course, no FADEC.

I do understand the generic rule---once stabilized, lean as long as EGT is increasing and engine is not turning rough, then add to be a little richer so that it runs smooth and happy.

I want to understand the generic appropriate mixture response to varying conditions---not precisely quantitatively, but directionally. how should the optimal (better) mixture change (holding everything else constant) with:

* an increase in altitude and/or temp ?
* an increase in throttle (RPM) to speed up ?
* a decrease in throttle (RPM) to slow down ?
* climbing (with more throttle)?
* descending (with less throttle)?

any other condition changes that suggest themselves to a good "first automatic" response?

if someone can point me to figures that plot optimal mixture to conditions, I can read the first derivative off the graphs...

no time for a tutorial, but: a carb is designed to provide a constantly variable air fuel mixture based upon vacuum (pilots call it MAP) and air flow. The mixture adjust / red knob acts as gross limiter at the entry of fuel into the system, to lean the mixture level being delivered by the carbs metering system. It is a manual adjustment and most changes to vacuum / air flow will require re-adjustment of the mixture knob, at least to maintain the air fuel mixture level desired. It's originally designed purpose was to deal with the variable altitudes that airplanes see. The higher you go, the more you need to lean the mixture relative to what was needed at sea level.

If you have leaned to a bit rich of peak (what you described in your post) and then you push in the throttle in, you will get progressively leaner the more you push. At some point the engine starts missing and just stops. If you pull back on the throttle, you will get richer, but only back to the point of what the carb variably delivers. No issue of going too rich to create roughness; within reason of course. If you will now be cruising at this new setting, just re-adjust mixture as before.

thx.

so roughly (pun!) speaking, when I increase the throttle, I should simultaneously begin to push the mixture to richer; and when I reduce throttle, I should simultaneously begin to pull the mixture to leaner. fine-tuning to happen later.

throttle and mixture control should thus typically move in the same direction together.

I have an O-360 pusher with an Ellison. It has a different response from the carbs I have had before in that there is very little roughness at the extremely lean condition. The engine just slows down, down down. I lean as much as possible on the ground--almost to the aft mixture stop. On climb-out I lean to peak power passing 4000' MSl and keep adjusting to peak until above 8000 MSL where I lean as much as desired for the trip using WOT--from lean to very lean. At a lower altitude cruise, I reduce RPM to what I think is 75% power and also lean as much as desired. I do not richen for descents until get to the pattern, where I richen a bit but not to full rich. Full rich for go-arounds, of course. I never really look at EGT.

+1 with Kent

I have a 320 with an Ellison and operate in a similar manner to Kent, although I use EGT to get to my LOP target. My engine combo will give me a subtle surge at about one hertz if I get too lean - like beyond 100F LOP. Like Kent, it just slows down, down....I don?t like the surge, but during phase one I got to 150F LOP and all four kept firing. I don?t richeN in descent, I richen moderately into the pattern, and go full rich-ish turning base, depending on DA. On takeoff, I?ve found one turn lean for each 1000? of DA from full rich is a good rule of thumb for takeoff, two more turns as I climb past 4000? DA for a little more power, which gives me 100F to 150F ROP as the MP starts to drop with altitude.

Don?t be afraid to lean below 75% power.

My engine starts easily, hot or cold. I use primer on two cyls on first start and just full rich warm to hot.

related question---even on full leaning, my engine continues to sputter on and never really wants to shuts down. (it worries me a little, because it means I cannot be sure that it won't start up by accident if someone on the ground starts playing with the prop.) I thought it was a bug that needed to be fixed on the annual.

is this a normal aspect of the ellison carb?

My apologies to the OP. My comments were geared towards a carb. I didn't read your post well and didn't realize you had an Ellison.

Larry

iaw4 said:

related question---even on full leaning, my engine continues to sputter on and never really wants to shuts down.

Click to expand...

Yeah, mine too but put the throttle wide open and it will!

Just set the throttle to idle and turn the ignition off, there really is no need to use idle cut off. You will also know that the ignition switches are turning the ignition off.

A little time

Getting the idle mixture set just right took me a little time. Until then, I had the same not shutting down with mixture to cutoff, at least when the temperature was warm out. Until then I used either ignition off method or advanced the throttle method mixture cutoff. Both work just fine.