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  #1  
Old 06-13-2014, 01:59 PM
9Driver 9Driver is offline
 
Join Date: Dec 2006
Location: Fernandina Beach, FL
Posts: 61
Default 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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  #2  
Old 06-13-2014, 02:57 PM
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DanBaier DanBaier is offline
 
Join Date: Mar 2009
Location: Rochester NY
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Default

Carbs in synch?

Dan
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  #3  
Old 06-13-2014, 05:05 PM
9Driver 9Driver is offline
 
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Location: Fernandina Beach, FL
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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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  #4  
Old 06-13-2014, 05:13 PM
roger lee roger lee is offline
 
Join Date: Sep 2013
Location: Tucson, AZ
Posts: 322
Default

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.
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  #5  
Old 06-13-2014, 06:02 PM
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Jetguy Jetguy is offline
 
Join Date: Aug 2008
Location: Texas, Fort Worth
Posts: 1,237
Default

Quote:
Originally Posted by 9Driver View Post
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
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?
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  #6  
Old 06-13-2014, 07:50 PM
Mike H Mike H is offline
 
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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  #7  
Old 06-13-2014, 07:58 PM
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RV3bpilot RV3bpilot is offline
 
Join Date: Oct 2012
Location: New Ulm, Minnesota
Posts: 283
Default 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....
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  #8  
Old 06-14-2014, 03:58 AM
N223JH N223JH is offline
 
Join Date: Apr 2008
Location: Boerne, TX
Posts: 228
Default

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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  #9  
Old 06-14-2014, 04:32 PM
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RDOG RDOG is offline
 
Join Date: Apr 2009
Location: Propwash Airport (16X), Texas
Posts: 136
Default Rough engine

Read this thread.http://www.vansairforce.com/communit...d.php?t=113585
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  #10  
Old 06-14-2014, 11:04 PM
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Special Delivery Special Delivery is offline
 
Join Date: Feb 2007
Location: League City, TX
Posts: 595
Default 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 View Post
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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