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  #21  
Old 08-05-2021, 04:59 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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With COVID this past year, I havenít flown in my friendís RV-12. We fly Loose formation a lot and compare temps while chit-chatting on 122.75. His exhaust temps are always 100F higher than mine at cruise power settings. His engine is always in mid to high 1400ís EGT.
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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 717

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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  #22  
Old 08-06-2021, 04:52 AM
todehnal todehnal is online now
 
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Location: Kentucky Lakes area in KY
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Thanks Jim for the photos and input. Yesterdays short flight was on an 80 degree day with CHTs around 190 and EGTs about 1340 L and 1440 R. I think the fouled plugs come later, after the lean mixture and high temps cause them to deteriorate. Then the roughness gets worse, the carbs shake and flood the cylinders causing the oil to turn black. And yeah, this all happens in 6 to 8 hours. Frustrating! I may do another smoke test to see if I can identify another intake leak. I have new intake manifold "O" rings and I may just go ahead and replace them as well. but that will have to wait until Saturday morning......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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  #23  
Old 08-06-2021, 08:11 AM
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Piper J3 Piper J3 is offline
 
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Per your photo in post #11Ö check rubber hose for cross-over balance tube. Hose appears to have a bend and I think it should be fairly straight routing. Also, the hose clamp on the manifold fitting is very poor quality as supplied by Rotax. I suspect a vacuum leak is possible at this location. When I installed High Performance Silicone heater hoses, I replaced this clamp. You can search 5-year Replacement Rubber Thread and find my posts.

O-ring for rubber carb socket maybe squished flat over time so replacement with new is good discission. As mentioned in previous post, you can use O-ring silicone grease very sparingly if concerned about sealing.
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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 717

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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  #24  
Old 08-06-2021, 02:53 PM
todehnal todehnal is online now
 
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Thanks Jim, Good stuff........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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  #25  
Old 08-07-2021, 12:43 PM
todehnal todehnal is online now
 
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I may have been premature in saying that I didn't solve anything by fixing the intake leaks at the drip tray socket connections. It did make a difference in the carb balance effect, and the idle. Yes, I still have a high EGT on the right bank, but that needs more explanation. First, sometime back during a 1 hour breakfast fight, I noticed a sudden change in the exhaust tone. It startled me, but the engine seems to continue to run fine, it just had a deeper tone. I pulled the muffler and shook it, but found nothing loose inside, so I reinstalled it and continued to run it. Very shortly after that I started having rough running, eating spark plugs and having very dirty engine oil. I chased my tail with carb rebuild, ignition system swaps and finally leading to an intake leak that seems to be behind me now.

Today, I pulled the spark plugs for a read after only about a 30 minute run yesterday. They were all burning quite evenly, although a bit sooty, which has been normal. So I took it for a test flight. At idle both EGTs are normal. Even up to 3000 RPM they remain pretty close. After takeoff I noticed the sharp increase on the right EGT, which is on cylinder #2. Retarding the throttle had little effect. With power retarded, and with the nose pointed down hill to raise the RPM I still have high right EGT. The only way to reduce the EGT reading is to reduce the engine RPM. In this case, just raising the nose and not touching the throttle, which reduced the RPM did the trick.

So, is there any way that a shifted baffle inside the muffler could cause such a condition. And if it could, is there any way to test it, other than paying $1300 for a replacement test muffler? I think that I may just be on to something here. Any thoughts appreciated.....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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  #26  
Old 08-07-2021, 02:25 PM
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Piper J3 Piper J3 is offline
 
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As mentioned above... higher (100F) EGT on right side is seen by lots of folks running 912ULS in RV-12 when engine is making high power. I wouldn't worry about it.
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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 717

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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  #27  
Old 08-07-2021, 05:07 PM
Mich48041 Mich48041 is offline
 
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Read what Mike Busch has to say about EGT:
https://resources.savvyaviation.com/...s-debunked.pdf
Carbureted engines often have EGT spreads of 150 degrees or more.
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  #28  
Old 08-08-2021, 08:35 AM
vic syracuse vic syracuse is offline
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You might consider replacing the throttle springs with the newer ones, and take a look at the throttle lever wher it hits the stop. It could be the picture, but it looks like the stop has worn a slot into the throttle lever.

Vic
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  #29  
Old 08-08-2021, 09:59 AM
todehnal todehnal is online now
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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I really appreciate the comments from Jim, Mich and Vic. I now have both the torsion and a light pull springs on the carb throttle levers which overcomes any play in the cable movement resulting in excellent carb balance. I guess my fixation with the EGT disparity is the fact that I am seeing a huge change from what they used to read. I have a lot of respect for Mike Busch and I read the listed article thoroughly. The other issue is that I am having a hard time wrapping my head around the fact that my high EGT reading worsens with RPM, not throttle. Also, as the EGT goes up, so does the vibration. That is why I was leaning toward a restricted airflow through the muffler. My next move is to make a runup test with, and without the muffler to see if that effects the EGT balance. Of course, I can't cowl it with the muffler off, nor fly it with the cowl off, so i am restricted to information gathered form ground runs. Also, that change in engine sound during a cruise flight is still haunting me. I'll report my findings.
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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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  #30  
Old 08-08-2021, 10:34 AM
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bshawco bshawco is offline
 
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Location: Near Durango, CO
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Not sure what fuel you're running, but I've recently seen a couple EAA LSA Webinars on the Rotax 912 that describe lead collecting in the muffler when using Decalin with 100LL. This unexpected side-effect cut the life of the muffler in half and required a replacement muffler. For that reason, the webinar host (Paul Shuch) now advises against using Decalin. This may not apply to your scenario, but I thought I'd mention it since you suspect a possible muffler issue.
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Last edited by bshawco : 08-08-2021 at 11:35 AM.
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