IO550 hiccup at low power. Too Rich?

SixPapaCharlie

SixPapaCharlie

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POH says something along the lines of full rich, fuel pump on when entering the pattern.

On final, I get down to around 15% power and without fail, the engine shutters periodically.

I am wondering if "full rich" may be the issue.
Normally as I descent, I watch the temps and enrichen ever-so-slightly to keep everything in harmony.

So around TPA in Dallas, My mixture is still somewhere around half. Enter downwind and go full rich, then further reduce power.

1. Could being too rich, cause this shutter?
2. If so, why not just baby the mixture as needed and land with the mixture where it was when I got to TPA?
 
Why full rich?

I'd keep her leaned for the field altitude, slowly twist it rich, never push it in to go rich, only time I'd use the button vs the veneer was to aggressively lean for ground ops and for shutdown. I also didn't normally kick on the pumps like that, kept the MP in the green till I was on final with the runway made before dropping MP below the green
 
Does it not do it if you lean it? On my Lycoming 0360 too rich causes backfiring (explosions in the exhaust) on pulling the throttle back. Thats typical.

Keep it lean even lean it more, and see if it stops backfiring.

You want to go to the richness that you take off at eventually, that is to prepare for go around. So If it does stop backfiring when you lean it, you are going to have to richen it to complete your GUMPS.

Also, carb heat richens the mixture.
 
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Below 50% power you can lean it as much as you want for as long as you want and not harm the engine. At 15% power I'd assume the prop must be driving the engine and that may contribute to your stumble. If I'm leaned on approach I stay leaned until short final.
 
Yeah, keep it leaned all the way down from cruise. If it happens to get too lean to the point of hesitation (has never happened to me) when landing, give it a nudge of fuel to smooth it out. Upon plane cleanup I lean it to ground setting (near cutoff). If I have to go around, all things full forward.
 
The POH says full rich boost pump on? Odd, the Bo (I use the Bo instructions from which my boost pump and IO-550 came from) instructions which tell you to set the fuel flow based on altitude and to leave the boost off unless you have some indication that you're engine driven pump isn't up to it.
 
flyingron said:
The POH says full rich boost pump on? Odd, the Bo (I use the Bo instructions from which my boost pump and IO-550 came from) instructions which tell you to set the fuel flow based on altitude and to leave the boost off unless you have some indication that you're engine driven pump isn't up to it.
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I'll be damned.
Just double checked the POH. I lied. :(

My instructor and our SR22 checklists (published and home made) all say mixture rich. That is what I was taught in the 172 as well.

POH says "Lean as necessary"

Time to revise my process.
 
flyingron said:
The Bonanza fuel flow gauge is marked with "rich" settings at various altitudes. I guarantee it's richer than you need.
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My Bonanza has an altitude fuel compensating pump so it gets max power adjustment on the roll, then back rich in the climb, then LOP for cruise.....it stays there till shut down.
 
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