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  #11  
Old 01-15-2021, 12:21 PM
trecool44 trecool44 is offline
 
Join Date: Oct 2020
Location: Weirsdale
Posts: 16
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Update, the carbs have been overhauled by Lockwood and reinstalled. The problem still exists to the same extent. I believe it to be an ignition issue. Any ideas about testing ignition components and procedures. Any input will help as the problem has been persisting for weeks now. Thank you.
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  #12  
Old 01-15-2021, 01:22 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,228
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You check ignitions in-flight and they are OK. Excuse me for saying so, but still sounds like a carb problem...
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #13  
Old 01-15-2021, 01:43 PM
trecool44 trecool44 is offline
 
Join Date: Oct 2020
Location: Weirsdale
Posts: 16
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I have done in flight ignition tests and everything seems fine. Its fine on the ground after the flight while doing a 4000 rpm test. Something is happening during the warmup from cold. One spark plug is just not firing on ignition B during the first attempt at the ignition test.
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  #14  
Old 01-15-2021, 03:01 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
Posts: 2,228
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You installed all new plugs? if so, you might consider replacing the spark plug caps. Just a feeling the 5 ohm resistor gets mutilated when pulling off the soft rubber caps - just a gut feeling. I installed these... https://www.ebay.com/itm/NGK-Spark-P...kAAOSwcP5c13Bx
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H

Last edited by Piper J3 : 01-15-2021 at 05:24 PM.
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  #15  
Old 01-20-2021, 09:29 AM
ChrisRV12new ChrisRV12new is offline
 
Join Date: Jan 2021
Location: Federal Way
Posts: 7
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I have this exact same issue. Any resolve? It started a few weeks ago. Replaced spark plugs and used Walker P12. Did not resolve issue. Flight ignition tests drop only 80 RPM. Initial warm up from cold engine 4000 RPM drop 400-500 and very rough running engine.

Also noticed very high fuel burn first hour of flight. 7.0 gph at 8300ft. Then very suddenly, it dropped to normal 4.4 gph. I donít know if this is related?

Are the plugs being fouled on cold taxi out? Really started when it got cold last few weeks.

New RV12 owner, very much still learning the aircraft. Any insight would be greatly appreciated.
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  #16  
Old 01-20-2021, 10:19 PM
whity1231$ whity1231$ is offline
 
Join Date: Dec 2020
Location: Eugene OR
Posts: 4
Default Rough running on first run up

I think your right on some plugs being fouled from a long taxi. I used to have the same problem. If your carbís are balanced, then Iíve found if you keep the time between start and run up as short as you can it helps.(2300 + rpmís till oil 120 degrees) Do the run up even if itís not where you normally do it, then do it again before take off. Hope it helps.
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  #17  
Old 01-20-2021, 10:35 PM
whity1231$ whity1231$ is offline
 
Join Date: Dec 2020
Location: Eugene OR
Posts: 4
Default Whity1231$

I think you are right about some plugs fouling from a long taxi. I used to have the same problem and found that if I keep the time from start to run up as short as possible it helped a lot.(2300 + rpmís till oil 120 degrees) Then run up even if not where you normally do, then again before take off.Hope it helps. Also make sure your carbí have been balanced.
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  #18  
Old 01-21-2021, 02:27 PM
trecool44 trecool44 is offline
 
Join Date: Oct 2020
Location: Weirsdale
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I have found a spark plug connector that looks to have some internal damage (resistance still checks ok) and looks to have been arcing inside the boot. New one is arriving today and will be installing and carb rebalance tomorrow. I will update when I have results. Thank you.
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  #19  
Old 01-22-2021, 09:36 PM
ChrisRV12new ChrisRV12new is offline
 
Join Date: Jan 2021
Location: Federal Way
Posts: 7
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What spark plug connector did you purchase? I printed off section 74 of the heavy maintenance manual. Looks like the spark plug boots screw on and off? Iím really new at this so my questions are pretty basic.

What I am having trouble understanding is why my RV 12 ignition check works after takeoff? 80 RPM drop in the air. On the ground, cold engine warmed up to 120 degree F oil temp and I get 500 RPM drop and feels like at least one cylinder not firing. Confused.

Good luck with your fix, hope it works. I will look at doing the same thing. Replaced all 8 spark plugs. Old ones were black and sooty.

Thanks- Chris
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  #20  
Old 01-23-2021, 11:05 AM
trecool44 trecool44 is offline
 
Join Date: Oct 2020
Location: Weirsdale
Posts: 16
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So the new spark plug boot and plugs did not help. The boots are NGK VD05FMH to match the originals, I got them Amazon. I also switched the ignition modules and found that the issue is still there when the A ignition is turned off during the check. This means that the issue is staying with the particular cylinder (#2). Has anyone switched coils for diagnostic purposes? I’m not how you would switch the coils on that cylinder for another cylinder to see if the issue remains.
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