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06-04-2017, 03:45 PM
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Join Date: Sep 2006
Location: Windsor, California
Posts: 924
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Since it appears appropriate to now "think out of the box": Is your tachometer accurately reflecting engine RPM? Are you hearing and feeling these power reductions or are you just observing changes in the tachometer reading? It wouldn't be the first time that the ROTAX/SV tachometer connection was a bit erratic.
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 940+ hours (as of September 2020)! 
V AF donation through June 2021.
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06-04-2017, 04:11 PM
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Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,065
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Quote:
Originally Posted by Azjulian
its the new vented tank
the vent line terminates near the base of the filler neck, but the return line terminates right next to the fuel output on the bottom of the tank
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The return line continues inside of the fuel tank and actually terminates pointing upward into the bottom of the fuel filler neck - at least that is the original design with vented cap. I'm pretty sure the return line is still routed the same way. So maybe you can look down the filler neck and verify that fuel is actually returning to the tank unimpeded. That would be good to know in your case...

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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 622 
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 : 06-04-2017 at 04:23 PM.
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06-04-2017, 11:14 PM
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Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 189
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Jim - of course now I understand what you mean, yes I will check that tomorrow.
David - yes its the engine note change that really gets your attention and you can hear it stumbling with a bit of vibration, but I would have said the vibration is minor.
Its more of a concern of is this going to become something else....
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06-05-2017, 07:35 AM
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Join Date: May 2013
Location: Temecula, CA
Posts: 295
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Is it possible that one of the ignition modules is going back into "soft start" mode randomly? Would not hurt ruling that out.
Alex
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Alex Erdelyi
RV-9A Purchased
RV-12 Built and Sold
Paid through December, 2020
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06-05-2017, 08:24 AM
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Join Date: Sep 2006
Location: Windsor, California
Posts: 924
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"Outside the box again": Could you have messed-up one of your spark plug connectors? Or not fully seated them on the spark plugs? They are relatively fragile if handled incorrectly. Do not install them by pushing down hard on the top of the connector -- push down along the sides -- see link to CT Flier site.
http://ctflier.com/index.php?/topic/...wn/#entry57273
__________________
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 940+ hours (as of September 2020)! 
V AF donation through June 2021.
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06-05-2017, 07:46 PM
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Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 189
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I just did some testing on my fuels lines and ran fuel for 5 mins at each point
Before mechanical fuel pump
28 gph displayed on gauge
I filled 2.4 gallons in 5 mins
Outlet of mech pump (21.4 gph displayed on gauge)
I filled 1.75gallons in 5mins
Left carb at union
(15.8 on gph displayed on gauge)
I filled 1.25 gallons in 5 mins
(I can confirm my fuel cube is accurate !)
I also check my spark plugs, all slightly off white
I check the integrity of my spark plug leads and connectors alll good.
I scoped down the fuel filler neck and I see a good spray on the return line.
I also check that I got no difference between running for 5 mins with hose off at mechanical pump and fuel cap on and off and there is no difference
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06-07-2017, 08:34 AM
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Join Date: Oct 2012
Posts: 421
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Quote:
Originally Posted by Azjulian
I just did some testing on my fuels lines and ran fuel for 5 mins at each point
Before mechanical fuel pump
28 gph displayed on gauge
I filled 2.4 gallons in 5 mins
Outlet of mech pump (21.4 gph displayed on gauge)
I filled 1.75gallons in 5mins
Left carb at union
(15.8 on gph displayed on gauge)
I filled 1.25 gallons in 5 mins
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The PAP requires "at least" 1 gal in 180 seconds from the output from the gascolator.
As an aside I was finishing my "annual" and noticed one float was sinking/ borderline - and during the run-up, fuel was leaking from that carb. Another sinker - new ones are 100/pair. Hopefully that will be it.
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06-08-2017, 09:58 PM
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Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,820
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Julian,
My carbs are at CPS for overhaul. When I get them back come over to GEU and you can try them.
Rich
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06-17-2017, 03:17 PM
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Join Date: May 2017
Location: Elberta, AL
Posts: 56
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did you ever find out what was causing the problem?
__________________
RV-14 SN 140398
emp & wings complete
fuselage in progress
N70C reserved
Flying out of 82J
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06-19-2017, 05:44 PM
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Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 189
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I'm pretty certain I have solved it, but I need to do a flight test and it is too hot here right now (120F). But I will report back
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