O-320 way rich after Major + 160HP conversion + Powerflow

On Thu, 1 Apr 2004 18:42:17 -0500, "Dave Gribble"
wrote:

This is the exact procedure we've used to set the mixture. The idle is 650
rpm and the increase when you move to cut-off is only about 25 rpm.

The problem is that it still seems too rich, especially in the pattern with
carb heat on.

Then there is something else going on besides the mixture adjustment. Have
you checked with the folk that hold the STC for the engine and exhaust
mods?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On 1-Apr-2004, wrote:

Yes, but think of the mixture knob as an "absolute" metering
adjustment, not a "relative" adjustment. In other words, setting the
mixture doesn't set
the air/fuel ratio... basically just the maximum amount of fuel that
can flow.


I'm afraid this doesn't make any sense. The mixture control DOES control
air/fuel mixture -- hence the name. If it simply controlled fuel flow the
mixture would change radically every time you touched the throttle. In
fact, what is controlled by the red knob (mixture) is the ratio of air
volume to fuel volume. As density altitude increases (i.e. air density
decreases), a greater volume of air is needed to mix with a given volume of
fuel for optimal combustion, so one has to lean the mixture (increase air
volume/fuel volume ratio).

-Elliott Drucker

On 1-Apr-2004, Ron Rosenfeld wrote:

No experience with the O320, but with the Lycoming O360's, the procedure
to
set proper mixture should be doable on the ground.

1. Start engine and warm up until CHT's and oil temps are normal.
2. Mag check -- if normal, proceed.
3. Set throttle set screw so idle is per airframe mfg recommendation.
4. Slowly move mixture control towards idle cut-off and observe rpm. An
increase of more than 50 RPM indicates the mixture is too rich. (An
immediate decrease, if not preceded by a momentary increase, indicates the
mixture is too lean).
5. When performing step 4, don't let the engine cut out.
6. Adjust the mixture control in the proper direction; run up to 2000 RPM
to "clear" the engine, and repeat the above as necessary. If the mixture
change has changed the idling RPM, that should be re-adjusted as needed.
7. If the setting does not remain stable, check the idle linkage for
looseness.


If the goal here is to set the mixture control linkage so that "proper"
mixture occurs with the control at the full lean position, then this had
better be done at or near sea level density altitude. How is the procedure
done on the ground in Denver?

--
-Elliott Drucker

No, that will be next. I think there are actually 2 STCs, one for the
exhaust (Powerflow) and one for the 160 HP conversion (Superior Air Parts, I
think). I wonder if the problem is in combining these 2 STCs?

"Ron Rosenfeld" wrote in message
...
On Thu, 1 Apr 2004 18:42:17 -0500, "Dave Gribble"
wrote:

This is the exact procedure we've used to set the mixture. The idle is
650
rpm and the increase when you move to cut-off is only about 25 rpm.

The problem is that it still seems too rich, especially in the pattern
with
carb heat on.

Then there is something else going on besides the mixture adjustment.
Have
you checked with the folk that hold the STC for the engine and exhaust
mods?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Fri, 02 Apr 2004 01:52:36 GMT, wrote:

If the goal here is to set the mixture control linkage so that "proper"
mixture occurs with the control at the full lean position, then this had
better be done at or near sea level density altitude. How is the procedure
done on the ground in Denver?

I don't know. All the manual says is that an "allowance" should be made
for setting idle for weather conditions and field altitude. It doesn't
state how to compute that allowance.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Thu, 1 Apr 2004 22:15:16 -0500, "Dave Gribble"
wrote:

No, that will be next. I think there are actually 2 STCs, one for the
exhaust (Powerflow) and one for the 160 HP conversion (Superior Air Parts, I
think). I wonder if the problem is in combining these 2 STCs?

I suppose it could be. But the 160HP converted engine should be listed as
an allowable engine for the Powerflo system. Or vice versa.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

wrote:
: I'm afraid this doesn't make any sense. The mixture control DOES control
: air/fuel mixture -- hence the name. If it simply controlled fuel flow the
: mixture would change radically every time you touched the throttle. In
: fact, what is controlled by the red knob (mixture) is the ratio of air
: volume to fuel volume. As density altitude increases (i.e. air density
: decreases), a greater volume of air is needed to mix with a given volume of
: fuel for optimal combustion, so one has to lean the mixture (increase air
: volume/fuel volume ratio).

OK... I'll concede that I oversimplified a bit.... The air/fuel ratio (as
in mass-air/fuel, like 12.5:1, 14:1, etc) does change when the throttle is moved.
Even without changing altitude, if the mixture is set to peak EGT, for example,
increasing MP by an inch will lean the engine (unless it's starting to enter the
full-throttle fuel enrichment regime). It's probably somewhere between the two
extremes (absolute fuel vs. relative fuel).

-Cory
--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

On Fri, 2 Apr 2004 13:59:49 +0000 (UTC),
wrote:

OK... I'll concede that I oversimplified a bit.... The air/fuel ratio (as
in mass-air/fuel, like 12.5:1, 14:1, etc) does change when the throttle is moved.
Even without changing altitude, if the mixture is set to peak EGT, for example,
increasing MP by an inch will lean the engine (unless it's starting to enter the
full-throttle fuel enrichment regime). It's probably somewhere between the two
extremes (absolute fuel vs. relative fuel).


Actually, you hit it pretty close. You do need to remember that aside
from the mixture control (and probably a crude economizer circuit), we
are talking about a one-barrel gasoline tractor carburetor.

On a MS carb, the "mixture control" is a chunk of brass on the end of
a two inch piece of flex cable (similiar to a tach cable). The mixture
knob rotates an arm clamped onto the top of the cable, rotating the
piece of brass on the bottom.

This piece of brass is stuck inside a brass cup on the bottom of the
fuel bowl with a "window" in it. At ICO, the window is "shut", at full
rich, the window is wide open.

The fuel gets sucked by the venturi out of the bottom of the bowl,
through the window, and out the main metering nozzle on the carb into
the induction airstream. The combination of the venturi type and the
main metering nozzle determines how much suction (relative to the
ambient pressure in the fuel bowl and the float/fuel level) is
generated "through" the valve.

Throttle plate position/engine rpm will indeed vary airflow through
the venturi, and consequently will affect the amount of suction. But
as you've indicated, the mixture control is a manually variable (with
the mixture knob) mechanical restriction to this suction. There is no
mechanical interconnect between the mixture valve and the throttle.

TC