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08-31-2018, 04:08 PM
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Join Date: Apr 2012
Location: Collierville, TN (KFYE)
Posts: 1,433
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Idle Mixture Adjustment?
I am helping a friend get his plane ready for first flight and we had to cancel today because the engine won't run reliably or smoothly at idle.
Details: Titan IO-360, Precision Silverhawk injector, EFII ignition.
Symptoms: Engine runs fine at higher RPMs, but dies when pulling throttle to idle with light backfiring and rough running just before quitting
Question, I figure the culprit is a misadjusted idle mixture. Should we go richer or leaner? I am thinking leaner. What ye think? Any other adjustments suggested?
__________________
RV-8 #81077 Super Slow Build
Dynon Skyview HDX, Titan IOX-370, Dual P-Mags, AFP FM200A FI, Whirlwind 200RV CS Prop
First Flight 11/20/2016
www.marksrv8.com
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08-31-2018, 05:37 PM
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Join Date: Jul 2018
Location: Naples fl
Posts: 140
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Idle
I would get someone familiar with the adjustment to look at it before a first flight, it is no time to be dealing with a cranky engine.
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08-31-2018, 05:37 PM
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Join Date: Jun 2006
Location: 8I3
Posts: 3,564
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Lean. Its backfiring because there's unburnt fuel in the exhaust. You want a 50 rpm rise like a carb when you pull the mixture.
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Please don't PM me! Email only!
Bob Japundza CFI A&PIA
N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
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08-31-2018, 09:39 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Backfiring during deceleration is typically due to an overly lean idle mixture. It is technically called an after fire, not a backfire and is caused by the lean condition creating intermittent misfires that place an unburned fuel air mix in the exhaust. The next combustion event that properly fires, ignites the mixture in the exhaust pipe. You have to be REALLY rich to get afterfires from a rich mixture.
The Bendix or Marvel manual should give a recommended starting position in number of turns out from fully seated.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 08-31-2018 at 09:44 PM.
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09-01-2018, 03:42 AM
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Join Date: May 2008
Location: Martinsville, IN
Posts: 454
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Heads or tails?
The best part is that either answer could solve the problem.
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09-01-2018, 04:49 AM
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Join Date: Apr 2012
Location: Collierville, TN (KFYE)
Posts: 1,433
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Quote:
Originally Posted by lr172
Backfiring during deceleration is typically due to an overly lean idle mixture. It is technically called an after fire, not a backfire and is caused by the lean condition creating intermittent misfires that place an unburned fuel air mix in the exhaust. The next combustion event that properly fires, ignites the mixture in the exhaust pipe. You have to be REALLY rich to get afterfires from a rich mixture.
The Bendix or Marvel manual should give a recommended starting position in number of turns out from fully seated.
Larry
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I failed to note that this is on the ground. We never got the idle sorted out so the the flight didn't happen. The next thing will be checking everything out per the manual.
__________________
RV-8 #81077 Super Slow Build
Dynon Skyview HDX, Titan IOX-370, Dual P-Mags, AFP FM200A FI, Whirlwind 200RV CS Prop
First Flight 11/20/2016
www.marksrv8.com
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09-01-2018, 08:40 AM
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Join Date: Oct 2005
Location: Lakeland, TN
Posts: 197
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Too Lean likely
Thanks for the responses. This is my airplane. I sure wanted to go flying...
I am idling too low (~600), but also I do not get any rpm rise when leaning. The engine will idle smoothly that low, but only if the throttle is retarded slowly.
Per the Silverhawk manual I should be idling 700-750 and that is the first place to start. Also per the manual, ?an immediate decrease in rpm toward cut-off without a preceding increase indicates too lean of a mixture?.
It appears to me the first fix is to (1) set throttle idle stop to 700-750, (2) enrichen the mixture until I am getting (ideally) 10-50 rpm rise.
The issue became apparent following some high power run-ups with a couple of throttle jam accel/decel. The engine acceleration had no issues. The rapid decels to throttle idle would cause engine to die.
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RV-8 KFYE
Memphis, TN
donation given
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09-01-2018, 09:28 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by Mark Dickens
I failed to note that this is on the ground. We never got the idle sorted out so the the flight didn't happen. The next thing will be checking everything out per the manual.
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I was referring to RPM decelleration, not airspeed. When you pull the throttle from High power to idle, that is decelleration (prop is decellerating) even on the ground.
Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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09-01-2018, 09:31 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by clam
Thanks for the responses. This is my airplane. I sure wanted to go flying...
I am idling too low (~600), but also I do not get any rpm rise when leaning. The engine will idle smoothly that low, but only if the throttle is retarded slowly.
Per the Silverhawk manual I should be idling 700-750 and that is the first place to start. Also per the manual, ?an immediate decrease in rpm toward cut-off without a preceding increase indicates too lean of a mixture?.
It appears to me the first fix is to (1) set throttle idle stop to 700-750, (2) enrichen the mixture until I am getting (ideally) 10-50 rpm rise.
The issue became apparent following some high power run-ups with a couple of throttle jam accel/decel. The engine acceleration had no issues. The rapid decels to throttle idle would cause engine to die.
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You may find that richening up the mixture will bring your RPMs up near 700 if you are as lean as I think you are.
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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09-01-2018, 09:38 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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You can download a manual for the silver hawk and it will cover all the details of how to set the idle mixture.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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