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  #11  
Old 08-05-2021, 04:31 AM
todehnal todehnal is offline
 
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Location: Kentucky Lakes area in KY
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Quote:
Originally Posted by olegusan View Post
I wonder why the drip tray installed between the rubber socket and the intake?
this may not have been the best choiceo attach it on other side of the rubber socket keeping it in place with the same bolts as the socket?

I agree that this may not have been the best drip tray mounting choice. Some Rotax powered aircraft do mount their drip trays without effecting the carb seals. I'm hoping that the added gasket, that was recomended by a Rotax rep at Oshkosh will solve the sealing problem. I will post the results....Tom
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  #12  
Old 08-05-2021, 04:40 AM
todehnal todehnal is offline
 
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Quote:
Originally Posted by Piper J3 View Post
When manifold leakage is fixed please report back on vibration, short spark plug life and very dirty oil. I'll be interested if fix solves any of these problems...
Jim, I will post the results. One other symtom that I didn't mention was that I have higher than normal EGT reading. In fact, occationally I have seen them up in the yellow zone, intermittantly and for short periods on the Skyview display at certain power settings.
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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
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  #13  
Old 08-05-2021, 09:35 AM
DHeal DHeal is offline
 
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Location: Windsor, California
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I suspect that it doesn't make much difference but according to the KAI (Page 46-07) the carb-to-rubber socket attachment clamp should be installed as follows:

Step 4: Install the band clamp (C) onto the carburetor flange assembly. See Figure 4. The clamp lugs and screw must be placed at the bottom or 6 o'clock position with the screw head facing outboard.
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  #14  
Old 08-05-2021, 10:53 AM
todehnal todehnal is offline
 
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Like you david, I don't think that it would make any difference, but that is the that I had them, and will do them this time as well....Tom
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1989- RV-6 tail kit, built and sold
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  #15  
Old 08-05-2021, 01:04 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by rvbuilder2002 View Post
I would suggest using extreme care in reassembling as illustrated in the parts manual (IPC)
I know of at least one engine that was destroyed because of a bad induction leak when the o-rings were installed on the same side of the drip tray as the carb socket.

The RV-12 ULS KAI specifically shows the o-ring on the manifold side of the drip tray, and nothing additional added on the carb. socket side.
The standard carb. socket has an integral o-ring molded into it which takes care of sealing on that side (unless you introduce a second o-ring that cant be kept in the proper position).

EDIT - I just looked through our archive of superseded Rotax documentation and found that in the 2010 version, it also showed a gasket but it was co-located with the o-ring on the manifold side of the drip tray.

Additional edit - I have an e-mail out to our USA Rotax tech. support contact. I will post here what I find out.
Response received <pasted below> and the answer was just as I suspected.

Dear Scott,

Glad to hear from you and I do remember this person, we suggested he inspected that area due to his complaint

I don’t think the IPC is correct, I agree with you that the O-ring needs to be on the manifold side, the gasket should be between the O-ring and the heat shield

I will get Rotax to comment on this, please continue doing as you were, I would only add the gasket

I hope this helps and I will let you know when Rotax comments

Best regards
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  #16  
Old 08-05-2021, 01:18 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by todehnal View Post
I agree that this may not have been the best drip tray mounting choice. Some Rotax powered aircraft do mount their drip trays without effecting the carb seals. I'm hoping that the added gasket, that was recomended by a Rotax rep at Oshkosh will solve the sealing problem. I will post the results....Tom
This drip tray mounting method is actually as designed by Rotax.
The depiction in the IPC is of the Rotax part # drip tray and how it should be installed (with the exception of what I believe is an error regarding the position shown for the o-ring).

A drip tray that mounted to the aft side of the carb. socket using the two mounting studs and nuts would be destroyed by vibration in a very short time because there is only room for it to have very small ears to attach at the studs.

There is now 700+ RV-12's flying, with the majority of them having the ULS engine. This is the first instance I am aware of where an induction leak at the carb socket was causing an engine performance problem when the parts were assembled as directed in the KAI.

How old are the carb sockets? They are one of the parts included in the 5 year rubber parts replacement schedule. If they have been replaced, were the new ones genuine Rotax parts or the aftermarket ones that are available?
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  #17  
Old 08-05-2021, 02:01 PM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
This is the first instance I am aware of where an induction leak at the carb socket was causing an engine performance problem when the parts were assembled as directed in the KAI.
I'm having a tough time figuring out how induction leak at both carbs is producing vibration, short spark plug life and very dirty oil as OP states.

I'll keep an open mind and wait for final report.
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Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 717

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  #18  
Old 08-05-2021, 03:04 PM
todehnal todehnal is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
This drip tray mounting method is actually as designed by Rotax.
The depiction in the IPC is of the Rotax part # drip tray and how it should be installed (with the exception of what I believe is an error regarding the position shown for the o-ring).

A drip tray that mounted to the aft side of the carb. socket using the two mounting studs and nuts would be destroyed by vibration in a very short time because there is only room for it to have very small ears to attach at the studs.

There is now 700+ RV-12's flying, with the majority of them having the ULS engine. This is the first instance I am aware of where an induction leak at the carb socket was causing an engine performance problem when the parts were assembled as directed in the KAI.

How old are the carb sockets? They are one of the parts included in the 5 year rubber parts replacement schedule. If they have been replaced, were the new ones genuine Rotax parts or the aftermarket ones that are available?
Hi Scott, Thanks for your research and response. I am fighting several issues. The most concerning is the high EGT on the right (1,3) bank. It is running about 100 degrees hotter than the left and may well be the cause of the spark plugs short life, followed by increased vibration, carb shake and flooding resulting in black oil. That led me to the smoke test in search of an intake leak. I installed new rubber carb sockets, "O" rings, and added the gaskets per the description that you sent. All parts are direct from Lockwood Aero. Additionally I installed new spark plugs and changed the oil, both of which only have about 8 hours on them. I also did a carb balance which dialed in perfectly. But I still have the high (100 degrees higher} right EGT than the left. These are new EGT probes and I have swapped them to verify that they are reasonably accurate. The engine is now running smooth at idle and in the mid 3000s, but I still feel a vibration at cruise, a well as off idle, even though the carb balance is right on. Both carbs recently went through a rebuild at Lockwood. Also the mag check is excellent. Cruise EGTs are roughly showing 1340 left and 1440 right. My test flight only lasted about 15 minutes, but I plan to pull the plugs in the morning to see if I can get a read on them. This is driving me crazy and has plagued me for more than 2 years now. Really appreciate your help............Tom
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1989- RV-6 tail kit, built and sold
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  #19  
Old 08-05-2021, 04:11 PM
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Piper J3 Piper J3 is offline
 
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I think most folks see higher EGT on right side – I do. I think perhaps the oil tank on the right side influences the right rear exhaust tube which is in close proximity.

Here are two photos of my D180 at different OAT’s. On the 37F day the right EGT is almost 100F higher than left. On the 67F day the EGT’s match more closely. For what it’s worth…
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Jim Stricker - EAA #499867
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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
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  #20  
Old 08-05-2021, 04:14 PM
NinerBikes NinerBikes is offline
 
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A vacuum leak usually generates a lean air / fuel mixture ratio. This would be inconsistent with fouled plugs and dirty motor oil in only 8 hours.

Some recent problems observed with Carburetors are rebuilt carbs by Lockwood, or CPS, don't remember which, with the chokes installed backwards, and poor epoxy on some very small fine ports on a couple of the Bing carburetors, that were generating air leaks and fuel mixture problems.

Do a Google search to see what shows up with those particular words in the search.
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