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  #1  
Old 04-20-2018, 10:56 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 918
Default Did I Break It?

Well, I guess if it ain't broke, I should leave it alone.
At the last inspection I noted that one of the floats was at 4.2. The others were at 3.1, 3.2, and 3.3. Total engine time was 315 hrs.

I had planned to install the new torsion throttle springs anyway, so I bought a full set of new floats and installed them at the same time. By the way, each new float weighted in at 3.2. I fired it up, warmed it up, and performed the carb balance. Everything was great and it ran terrific (smooth as glass). The next morning I was off for a breakfast fly-in, or so I thought. After warm up I did the normal ignition check and found Ignition A was faltering badly. I shut down and did the simple thing first. I swapped all of the plugs top to bottom and bottom to top. Sure enough, the problem moved to ignition B. I don't mess with iffy plugs, and even though this set only had 115 hours on them, I installed a new set. All was well, smooth as glass again and run up was great.

That brings me to this morning when I was planning a nice morning flight. Having just been through some issues, I was very attentive at startup, which seemed good with everything running smooth. After warm up I did the ignition test and all was good. I powered up for takeoff and noticed some stuttering, and promptly aborted the take-off. Additional ground run testing revealed that it is running very rough at almost any rpm, and ignition check shows no difference using A or B. So, I shut down and pulled it back into the hangar. A finger swipe in tail pipe revealed extremely heavy soot. I pulled the top plugs and found #1 and #3 totally black whereas #2 and #4 looked pretty good. Obviously the right carb is running way too rich. ***THIS WAS AN ERROR*** Actually it was spark plugs #1 And #2 that were sooty. #3 and #4 were the ones that looked pretty good. So it ain't the carbs!!! So, my last paragraph here doesn't hold up, but I left it for clarification.........

I think that I have identified the fact the the right carb is running rich. The problem is knowing why, and what happened? I'm not much of a believer in coincidence, so I am trying to figure out how I could have possibly caused this, or where do I go from here.? Any help will be greatly appreciated..... Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
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1989- RV-6 tail kit, built and sold

Last edited by todehnal : 04-20-2018 at 02:16 PM.
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  #2  
Old 04-20-2018, 11:04 AM
Mike S's Avatar
Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Default

Sounds like you might have gotten some crud under the needle while changing floats.

Or, possibly damaged the needle/seat?

Good luck with the sleuthing.
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Rv-10, N210LM.

Flying as of 12/4/2010

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  #3  
Old 04-20-2018, 11:42 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Default

Or one or both of the new floats you put in the right carb. could be bad.
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  #4  
Old 04-20-2018, 11:46 AM
DHeal DHeal is offline
 
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Location: Windsor, California
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Are carb bowl gaskets properly seated? Did you blow air through the orifice in the lower corner of the carb bowl to clean out any debris (I believe that orifice is part of the start/idle circuit but it wouldn't hurt to make sure it is free of debris)? Check that the right-side starting carb ("choke") is properly configured (i.e., spring, cable, etc.).
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Last edited by DHeal : 04-20-2018 at 11:51 AM.
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  #5  
Old 04-20-2018, 12:38 PM
alexe alexe is offline
 
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Location: Temecula, CA
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+1 for Scott. I was a recipient of NEW floats that sunk after a few days.
Alex
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  #6  
Old 04-20-2018, 02:11 PM
todehnal todehnal is offline
 
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Location: Kentucky Lakes area in KY
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Okay. I guess I am a little upset here, and I made a mistake in identifying the black spark plugs. Actually it is number 1 & 2 plugs that are all sooty. Now that is starting to look like an ignition unit. What I am having trouble with now is that the poorest ignition test comes when grounding A. According to the schematic, #1 & #2 are connected to ignition A, but that is where it ran the best

I did go ahead and pull and check the floats. They all look good and still weigh in at 3.2. There is no fuel on the drip trays, and the needles and seats appear to be functioning correctly. I really think that I may be looking at a bad ignition, but I'm not sure how to proceed from here.

I think that I will put it back together with clean plugs, do a run up, and shut it down from a high RPM, then re-examine the plugs. What stumps me is that both upper and lower #1, and #2 cyclinder plugs look sooty, while all #3 and #4 plugs look pretty good. Sorry for the confusion...........Tom
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1989- RV-6 tail kit, built and sold
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  #7  
Old 04-20-2018, 03:00 PM
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scottmillhouse scottmillhouse is offline
 
Join Date: Apr 2007
Location: Madison, AL
Posts: 217
Default Similar problem today

Watching this thread for ideas.

This is a older Rv-12 that had been sitting a few years but only has 70 hours. My friend bought and we did all upgrades, paint and service bulletins. Ground ran a few times on newly overhauled carbs with new floats. Ready to fly but waited due to defective fuel pressure sender and motor would only turn about 4800 static. Replaced sender and repitched coarse prop to Vans pitch. Motor was running rough, pulled carbs and flushed. Tried to run up but appears to both miss fire and run rich. Number 1&2 top black and wet (both appear to go to same coil). A ignition runs smooth but could only get about 3200, B very rough but could get about 4000 with or without A. My plane smooth as silk on either for one ignition over 4900. Thinking ignition but not sure where to start to trouble shoot.
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  #8  
Old 04-20-2018, 03:10 PM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Quote:
Originally Posted by DHeal View Post
Are carb bowl gaskets properly seated? Did you blow air through the orifice in the lower corner of the carb bowl to clean out any debris (I believe that orifice is part of the start/idle circuit but it wouldn't hurt to make sure it is free of debris)? Check that the right-side starting carb ("choke") is properly configured (i.e., spring, cable, etc.).
I very much appreciate the suggestions. I pulled the carbs again, weighed the floats, blew out the orifices, and verified all of the linkage. I think that I mis-identified the sooty plugs, and have now verified that they were #1 and #2. Sorry for my stupidity. It's just that I have totally enjoyed my 315 hours of superb performance, and now I am faced with a difficult problem, but I guarantee that someones suggestion will nail this thing, and I will be back at enjoying the fruits of my efforts. I need all of the help that I can get.
Thanks.......Tom
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2013- RV12, Kit #119. N123M First flight Nov21. It's a keeper!
1998- RV-9 tail kit, built and sold
1989- RV-6 tail kit, built and sold
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  #9  
Old 04-20-2018, 03:16 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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I wouldn't worry about rich appearance on #1 and 2.
That is pretty common if the engine has been run at idle or low power for a while before shut down (different mixture to front cyl because of intake man. shape).
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  #10  
Old 04-20-2018, 05:11 PM
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Phantom30 Phantom30 is offline
 
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Location: Coeur d'Alene, ID/Casa Grande, AZ
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Default

Not sure if you have tried this...but I would get a “new” set of plugs....also check plug wires (go for the easy stuff first). Put vacuum gauges on and check for leaks. Normally, it is something simple.

Also, check choke operation is right..
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Last edited by Phantom30 : 04-20-2018 at 05:15 PM.
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