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06-13-2014, 01:59 PM
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Join Date: Dec 2006
Location: Fernandina Beach, FL
Posts: 61
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Rough engine on takeoff roll
RV-12, 18 hrs, OAT 85. Flew the pattern three times, with a full stop, taxi back and takeoff. On fourth attempt, just prior to liftoff, engine became extremely rough. Aborted takeoff, taxied back to ramp. Did ignition check at 4000 - OK. Made three full power ground runs all resulting in a smooth running engine. Taxied back and started takeoff roll. Again just prior to liftoff engine became extremely rough. Returned to hangar, removed upper cowl and checked engine. No fuel smell, no apparent issues. Fuel pump and hoses very hot. Possible vapor lock? Apparently only occurs above static rpm range. This is first time to have just flown pattern.
Any help appreciated.
Thanks in advance
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06-13-2014, 02:57 PM
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Join Date: Mar 2009
Location: Rochester NY
Posts: 669
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Carbs in synch?
Dan
__________________
RV7A (N7101) - Flying 10/2008
CFI- SE/ME/Inst
A&P
KC2ZEL
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06-13-2014, 05:05 PM
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Join Date: Dec 2006
Location: Fernandina Beach, FL
Posts: 61
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As far as I know - I had already made three no problem takeoffs prior to the roughness.
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06-13-2014, 05:13 PM
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Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
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Since the mag drop was good (most likely not electrical) and the run ups are good then the next step is to pop the carb bowls off and take a look. These are common symptoms for a reduced fuel flow. Carb debris needs to be ruled in or out and the easiest place to look and is a common cause. Debris usually won't show up on a run up many times. Too long to explain, but will get in the main jet fuel flow at full throttle during a climb or flying.Don't look for exotic problems, I'll bet money it's an easy fix.
__________________
Roger Lee
Tucson, AZ
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06-13-2014, 06:02 PM
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Join Date: Aug 2008
Location: Texas, Fort Worth
Posts: 1,237
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Quote:
Originally Posted by 9Driver
RV-12, 18 hrs, OAT 85. Flew the pattern three times, with a full stop, taxi back and takeoff. On fourth attempt, just prior to liftoff, engine became extremely rough. Aborted takeoff, taxied back to ramp. Did ignition check at 4000 - OK. Made three full power ground runs all resulting in a smooth running engine. Taxied back and started takeoff roll. Again just prior to liftoff engine became extremely rough. Returned to hangar, removed upper cowl and checked engine. No fuel smell, no apparent issues. Fuel pump and hoses very hot. Possible vapor lock? Apparently only occurs above static rpm range. This is first time to have just flown pattern.
Any help appreciated.
Thanks in advance
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Get a fresh start in the morning. See if the problem has corrected itself. If the plane runs fine then it's heat related. How long was your taxi back between the last normal takeoff?
__________________
John
RV12 N1212K
Flying Since June 2010
1020 Hours as of 9/30/2017
Johnrv12@icloud.com
RV14 Wing, arrived and building at Rdog's new Hanger at 16X
S/N 140014
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06-13-2014, 07:50 PM
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Join Date: May 2014
Location: Savannah
Posts: 806
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The same has happened to me in another 912 powered aircraft. It is most likely fuel contamination. When you remove the bowls look very closely for ANY debris in the fuel bowl. Then remove the jets and carefully clean them and inspect them for blockage. It does not take much to stop up the main jet on a Bing carb.
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06-13-2014, 07:58 PM
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Join Date: Oct 2012
Location: New Ulm, Minnesota
Posts: 283
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Rough Engine on take off
I had a fuel filter that started to plug and would only act up when at full throttle long enough to make the engine go lean....
__________________
Robin Mckee
New Ulm, MN 56073
RV3b N219BB
420 hours and counting
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06-14-2014, 03:58 AM
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Join Date: Apr 2008
Location: Boerne, TX
Posts: 228
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In addition to the previous excellent suggestions...
Download flight data from your Dynon. You may see fluctuations in fuel pressure and fuel flow. Earlier RV-12's had the fuel pumps which were superceded by an improved one by Rotax. BTW, the fuel pump does not have to show signs of leakage to be partially inoperative.
One other thing to check with the top cowl off: Make sure your ignition modules are tightly grounded to those bolts on the intake manifold. If not, spark could be intermittent.
The above is not speculation; I experienced both in the first 50 hours.
Good Luck,
Jim
#264 flying 245 hours
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06-14-2014, 04:32 PM
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Join Date: Apr 2009
Location: Propwash Airport (16X), Texas
Posts: 136
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Rough engine
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06-14-2014, 11:04 PM
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Join Date: Feb 2007
Location: League City, TX
Posts: 595
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My Recent Experience
9Driver,
Been fighting this same/repeatable problem for a week now on a 100hr engine. Every indication (to me) was ignition breaking down at high temps... run-up and full power ok once, maybe twice, after reaching 122* oil temp, then 3800 max and missing at full power. Let it cool and repeated numerous times. Changed plugs, checked all grounds & plug wires etc., and no change. Based on low CHT on #2 and EGT on #4, and advice from Lockwood, I went ahead and pulled the left carb. Bowl was dishwasher clean and not a speck of debris. Removed floats needle/seat, blew out all jets, and re-installed. Never positively identified the problem, but it's GONE! Not a real confidence builder.
I believe Roger is spot-on in his diagnosis of your problem. Follow his lead and advice.
Have a great day!
Quote:
Originally Posted by 9Driver
RV-12, 18 hrs, OAT 85. Flew the pattern three times, with a full stop, taxi back and takeoff. On fourth attempt, just prior to liftoff, engine became extremely rough. Aborted takeoff, taxied back to ramp. Did ignition check at 4000 - OK. Made three full power ground runs all resulting in a smooth running engine. Taxied back and started takeoff roll. Again just prior to liftoff engine became extremely rough. Returned to hangar, removed upper cowl and checked engine. No fuel smell, no apparent issues. Fuel pump and hoses very hot. Possible vapor lock? Apparently only occurs above static rpm range. This is first time to have just flown pattern.
Any help appreciated.
Thanks in advance
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__________________
R. E. "Ernie" Butcher
Friends of the RV-1/Eagle's Nest Projects
"Mentors build the student...
Students build the airplane." -Glen Salmon
Dedicated to the historical preservation of the RV-1 Aircraft
and organized for the purposes of promoting, supporting,
fostering, and engaging in aviation and aerospace education.
www.RV-1.org
www.EaglesNestProjects.org
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