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  #1  
Old 08-31-2018, 04:08 PM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
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Location: Collierville, TN (KFYE)
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Default 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?
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  #2  
Old 08-31-2018, 05:37 PM
Tommy123 Tommy123 is offline
 
Join Date: Jul 2018
Location: Naples fl
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Default 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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  #3  
Old 08-31-2018, 05:37 PM
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rocketbob rocketbob is offline
 
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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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  #4  
Old 08-31-2018, 09:39 PM
lr172 lr172 is online now
 
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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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Last edited by lr172 : 08-31-2018 at 09:44 PM.
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  #5  
Old 09-01-2018, 03:42 AM
dtw_rv6 dtw_rv6 is offline
 
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Location: Martinsville, IN
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Heads or tails?��
The best part is that either answer could solve the problem.
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  #6  
Old 09-01-2018, 04:49 AM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
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Default

Quote:
Originally Posted by lr172 View Post
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
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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  #7  
Old 09-01-2018, 08:40 AM
clam clam is offline
 
Join Date: Oct 2005
Location: Lakeland, TN
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Default 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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  #8  
Old 09-01-2018, 09:28 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by Mark Dickens View Post
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.
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
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  #9  
Old 09-01-2018, 09:31 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by clam View Post
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.
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.
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  #10  
Old 09-01-2018, 09:38 AM
BillL BillL is offline
 
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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.
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