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09-08-2014, 10:59 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,297
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My advice (warning: I am a carb guy)
1) view the EAA video on adjusting idle mixture.
2) I believe your idle setting is too rich. Lean it a 1/4 turn (or 1/2 turn to start) via the idle mixture screw on the throttle body/servo (not the red knob) and repeat the test in the video. Keep doing this until you get the recommended behavior.
You are likely getting the large drop as you lean because your idle is very rich. I am guessing that you don't get much resolution with the mixture knob on the idle circuit (just a guess, I am a carb guy)
If you struggle much in getting it to behave, be sure to heed the previous posters advice about checking for induction leaks.
If you search, you will find solid descriptions of the test and interpretation for adjusting idle mixture.
Larry
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09-09-2014, 05:43 AM
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Join Date: Jun 2006
Location: 8I3
Posts: 3,564
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Sure sounds like the barrel valve is scored and leaking air, no amount of fiddling as you've already done will get it to idle right.
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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
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Not a thing I own is stock.
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09-09-2014, 08:21 AM
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Join Date: Jan 2007
Location: Battleground
Posts: 4,348
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It is a very simple procedure. If you can't dial it in easily per RSA instructions, there is something else wrong as others are suggesting.
I chased mine for some time and could never get it right. We tested for all the usual suspects, returned the servo (nothing wrong), you name it. It turned out to be a slightly sticky exhaust valve that was VERY difficult to diagnose.
At normal operating RPM's, like in climb or cruise, the combustion cycle is so fast that "minor" problems, like a slightly sticking valve, may not show themselves. However, at idle RPM, things are slowed down and those same problems can manifest themselves into a more obvious issue.
Nobody would have expected a slightly sticky valve to be something to look for as it is so unusual. I had multiple mechanic friends helping me. I found the issue almost by accident. I could not imagine what hiring a mechanic would have cost. (and I seriously doubt they would have found the issue.)
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09-09-2014, 08:27 AM
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Join Date: Nov 2006
Location: Saint Simons Island , GA
Posts: 1,523
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Quote:
Originally Posted by Mike H
Hang around a little longer and someone will surely start paraphrasing Mr. Busch and tell you that you are wasting time and money trying to maintain your aircraft and you should just look the other way, leave it alone and keep flying it  . Besides all A&P mechanics do is damage airplanes 
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Now that's a thought out and helpful reply.
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Jerry "Widget" Morris
RV 8, N8JL, 3,000+ hours on my 8.
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PIF 2008, 2009, 2010, 2011,2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020
 I just wish I could afford to live the way I do
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09-09-2014, 08:35 AM
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Join Date: Jan 2005
Location: St. Paul, MN.
Posts: 4,792
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I know this is kind of a stupid question, but you've checked to be sure the throttle arm is moving from stop to stop, right?
I ask that because I was sure mine was when I installed the Van's throttle cable but it turns out it wasn't because the standard arm that came with the servo was actually too long so I swapped it out for a smaller one from Precision and all the problems were solved.
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09-10-2014, 09:48 AM
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Join Date: Oct 2011
Location: Atlanta
Posts: 878
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Got some good pointers from Don at AFP yesterday. Great guy, spent 30 minutes on the phone with me for $0, and seems very knowledgeable. I'm really looking forward to the FI seminar this fall.
One of his first comments when I mentioned that I'd gone back to the RSA installation and operation manual and adjusted the starting length of the connection to 2.5" nominal as recommended in the manual, was to throw the manual away, its half nonsense.
Per his recommendation I'll be setting the starting point for the idle stop by setting a .006" gap between throttle plate and bore, and setting the starting point for the idle mixture by adjusting the linkage until I get a fuel flow (disconnecting the line before the flow divider) of 1.2 gph with throttle at idle, full rich, boost pump on. That is my starting point to start adjusting.
Don seems to think it is a possibility there may be another problem as well, but that I'm likely not too lean, but way too rich. Hopefully more info this weekend.
Thanks for the constructive insights.
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Last edited by walkman : 09-12-2014 at 01:27 PM.
Reason: Fixed fat finger
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09-10-2014, 11:01 AM
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Join Date: Jun 2006
Posts: 316
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Idle fuel flow
Start with .006 throttle opening, idle fuel flow to 1.2 GPH.
Then tune from that point as required.
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09-12-2014, 01:27 PM
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Join Date: Oct 2011
Location: Atlanta
Posts: 878
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Quote:
Originally Posted by Don at Airflow
Start with .006 throttle opening, idle fuel flow to 1.2 GPH.
Then tune from that point as required.
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Thanks for the correction Don. Meant 1.2 but hands had a mind of their own.
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RV-8 IO-360 (Bought)
RV-6 O-360 C/S (Sold)
Walkman aka Flame Out
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09-12-2014, 02:13 PM
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Join Date: Apr 2012
Location: Tampa (BKV)
Posts: 926
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I have spent my time with Don on the phone as well. He straightened me out on idle adjustment during my phase one. I'm not typically a "faithful" guy when it comes to purchases...but Airflow gets my fuel delivery business. Don and his people are a valuable resource.
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