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  #21  
Old 05-31-2017, 02:30 PM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 116
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Hi John - Good thoughts, out of that list here is what I have done so far.

I checked the gascolator and cleaned post first flight I had the issue. I did repeat the volume test by using the input line to the mechanical pump and was well within range. I'm going to repeat the test at the carb fuel fitting.

I talked to Lockwood and they suggested "borrowing" someones carbs from a known working setup to determine if this was a carb issue.

Julian
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  #22  
Old 05-31-2017, 03:45 PM
cactusman cactusman is offline
 
Join Date: Oct 2012
Posts: 421
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Quote:
Originally Posted by Azjulian View Post
Hi John - Good thoughts, out of that list here is what I have done so far.

I checked the gascolator and cleaned post first flight I had the issue. I did repeat the volume test by using the input line to the mechanical pump and was well within range. I'm going to repeat the test at the carb fuel fitting.

I talked to Lockwood and they suggested "borrowing" someones carbs from a known working setup to determine if this was a carb issue.

Julian
I would offer mine - but the plane is up north and I'm hoping to finish my annual this weekend.
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  #23  
Old 06-03-2017, 08:31 AM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 116
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Update 6/3/2017 - I completely re-setup my carbs after cleaning, both mechanically and them using a carb sync tool. It was very hot yesterday (over 100F) with a density altitude of 4500'. With the engine hot (CHTs over 200) and the hot OAT I was able to replicate the stumbling I have heard in flight. It's a little random being able to replicate, it can take some time holding WOT and then the issue can just go away, have to say this is extremely frustrating.

https://youtu.be/mS7NNFnSRrg
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  #24  
Old 06-03-2017, 10:36 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,523
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Have you adjusted the prop pitch yet? Lugging the engine is bad for it and makes it run hotter. If the engine still stumbles after fixing the prop pitch, consider installing a blast tube from the cowl duct to the left carburetor bowl.
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  #25  
Old 06-03-2017, 10:42 AM
Azjulian Azjulian is offline
 
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Location: Scottsdale, Arizona
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Hi Joe - yes I should have added that I flattened the pitch by 0.4 degrees which has increased my static rpm to 5350
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  #26  
Old 06-03-2017, 11:31 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 6,970
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Quote:
Originally Posted by Azjulian View Post
I got a chance to fly again this morning (6am and it was already 80F OAT)

The 100LL did NOT fix this issue, I didn't experience the issue on initial climbout but I did when transitioning to a WOT climbout from a slow flight test.

I did test my WOT cruise, it took some time but the max I could get was 5500RPM.

My static WOT is 5200, on my climbout i'm seeing my RPM dropping slightly as I climb, by 3000' AGL i'm at 5060RPM
It is going to be hard to help you when you ignore some information being provided.....

The static RPM you originally mentioned was fine or actually just a bit too high, but now you have reduced the pitch even more. You are now way under pitched.
I previously mentioned a serious discrepancy in the information you were providing..... that your static RPM on the ground was higher than what it is climbing after takeoff. This should never happen, so it is probably a major clue in solving your problem.

Like I said before.... you very likely have a carb. problem caused by contamination resulting from it being a newly completed airplane (very common). Lockwood even tried to head you that direction by suggesting you try a different set of carburetors. What process did you use to clean the carbs? It will require more than just removing and cleaning the float bowl.
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  #27  
Old 06-03-2017, 12:33 PM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
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Hi Scott - I apologize if you feel that I am ignoring advice. I'm actually trying to attack this in a very methodical way. On my last flight I checked exactly what you asked, with my 5100-5200 static WOT RPM that does change with temperature, I was seeing a slight increase in climb (about 50 or so rpm). On cruise WOT max RPM I could see on that day was 5500 with a density altidtude of around 6500'. I talked to both Lockwood and Roger Lee, who both suggested flattening the pitch by about 0.4 degrees, which I did. My mistake on interpretation of the static WOT was not do a same day direct comparison as I am seeing a slight difference in WOT static RPM from day to day depending on temperature.

To clean the left carb I removed the top and the diaphragm, the float needle and assembly. then used carb cleaner and compressed air and blew out every single orifice and jet. I took out the needle and check position and cleaned the assembly.

I did not clean the right carb to that extent yet as due to the EGT reading Lockwood and Roger Lee both felt that it was on the left side that I had the problem.


I also ran the fuel lines with the carbs off to ensure no contamination.

I then reassembled and started at the beginning of the carb chapter in line maintenance I setup the carbs from scratch, idle mixture, mechanical setup, the. I synced the carbs and did that sync from idle all the way up to WOT. They are now very balanced.

When I changed my prop I triple checked that my pitch on both blades to ensure balance.

Additionally I did squirt carb cleaner at the manifold and at the carb socket to see if I had a leak anywhere.
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  #28  
Old 06-03-2017, 06:36 PM
Azjulian Azjulian is offline
 
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Location: Scottsdale, Arizona
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Scott - can I confirm your concern, from your message I'm reading that you would expect the static WOT RPM to be lower than the climb WOT RPM and then that cruise WoT RPM ?

We are just not seeing that here, I had a friend who has an SLSA RV12 check and his ground static WOT is 5500RPM, at 75knt climb out he is seeing between 53000 and 5350. Then in level flight WOT he gets 5600
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  #29  
Old 06-03-2017, 07:09 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
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FWIW, here are my approximate RV-12 specs (with wheel pants): Ground WOT @ 4,950 rpm, Climb-Out WOT (@ 75 kts) @ 5,250 rpm, and Cruise WOT (@ 6,500' msl) @ 5,650 rpm. My Idle is set 1,650 rpm static on the ground and this results in @ 2,000 rpm on short final. I typically cruise at @ 5,250 rpm and see @ 108+ kts IAS.

IMHO, if your Ground WOT rpm is higher than your Climb-Out WOT rpm, then that sounds like an engine issue, not a prop pitch issue.
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  #30  
Old 06-03-2017, 07:18 PM
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scottmillhouse scottmillhouse is offline
 
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Location: Madison, AL
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I'd clean out the right carb too. It is not unusual to have the instrumentation switched between the right and left side. You may be troubleshooting the wrong carb. Easy to mistake if wiring from the front and using your right instead of plane right.
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