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300CBi mixture leaning?

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The fuel-injected 300CBi has a mass-airflow sensor so no leaning is required, the aircraft takes care of itself. Only at idle, with clutch disengaged can you perform an idle mixture check - otherwise mixture full rich and let the FI take care of everything.
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Hey Fling,


I totally agree with you but I'm looking at the Precision Airmotive Ops and Service manual for the RSA-5 FI.  According to it...


"As a rule of thumb, the engine consumes six pounds of air per brake horsepower regardless of altitude.  A volumetric air flow metering unit will enrich approx. 1.7 to 2.3 percent for every on thousand feet in altitude.  This enrichment variation depends on the specific altitude. Variations ar greater at higher altitudes."


"The direct reason for enrichment is the change in air density.  If altitude or temp. is increased it will require a greater air volume to flow the same weight of air into the engine.  This will increase the air metering forces and in turn increases the fuel metering forces resulting in a richer fuel/air mixture as altitude increases."


The RSA-5A"B"I has an automatic mixture control but the RSA-5A"D"I (which is what's on the CBi) doesn't.


Here's some more from the "Manual Leaning" section of the service manual...

"The setting incorporated in the injector satisfies the engine requirements for sea level operations.  As air density decreases (altitude) the throttle is opened to maintain the same power.  Opening the throttle causes a higher air metering force which, in turn, results in a greater fuel flow.  The manual mixture control may then be moved towards the cut-off position to reduce fuel flow to the desired value."


To me, that sounds like it doesn't lean the mixture automatically.

Let me know your thoughts.

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Dang it, there's ANOTHER manual I'm going to have to read...


Seems I was misinformed about the CBi's FI system. But since the PFM says no leaning, I don't lean. However, I've only flown the 300CBi at up to 4,000' DA or so. I know that EGT is available on the C model, with an associated leaning procedure, and of course the CB has a leaning procedure.


Hm. I'll have to get back to you.

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  • 2 months later...

The CBi doesnt need leaning as you guys have pointed out, but I was taught to lean the CBi after a marginal or failed mag check to raise the CHT (cyl.head temp.) to burn off carbon build up on the plugs. It doesnt always do the trick but it's worth taking the time as opposed to grounding the ship.

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