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  #1  
Old 03-22-2018, 05:06 PM
bob1393 bob1393 is offline
 
Join Date: Jun 2014
Location: Port Orchard, Wa
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Default Rotax 912 ULS Running Rough

I'm hoping Scott from Van's will jump in here and offer some ideas for us.

Last Thur, my wife and I, after doing a run-up in our RV12 prior to take off (run-up and all engine gauges perfect and in the green), Proceded to the runway, added power, and started take off roll. Everything fine until moment of lift-off. Engine starting running real rough, lots of vibration, loss of power. I immediately pulled throttle to idle and landed without any problem. Taxied off the runway (engine running great now) to a safe spot, then tried to do another run-up. Engine ran great until just under 4000 RPM, then ran rough again. It feels like the engine is missing or not running on all 4 cylinders. Tried several times with same result. Taxied to hangar and shut it down for the day.

The next day, my partner beat me to the hangar, he started it and it ran perfect. Even up to full power. He even flew around the pattern and did a couple of T&G with no issues. My partners and I have flown it several times this week with no problems.

I want to add that concurrent with the aborted take-off the Ducati VR failed. We replaced it. However, engine was running good when my partner started it before replacing the VR.

So the question is, can you Scott, or anyone else, provide any hints to us as to what we should check or look for? Would the VR failure cause it to run rough? When we started it the next day with a bad VR it ran great. BTW, engine has 445 hours, same as plane. Certified Oct 2015. Partner and I built it. Running flawless since certified.


Bob

Last edited by bob1393 : 03-22-2018 at 05:08 PM. Reason: Added engine hours.
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  #2  
Old 03-22-2018, 05:22 PM
DHeal DHeal is offline
 
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Sure sounds like a bit of debris in one of the fuel bowls temporarily blocked a jet. Right after the event, did you pull off the two fuel bowls and look for debris? Since the engine is now running OK the debris may or may not still be there. You can look at your Dynon engine performance print-out to see if there are any noticeable anomalies or trends. I do not think that your temporary rough engine issue is associated with the Ducati R/R.
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  #3  
Old 03-22-2018, 05:22 PM
mturnerb mturnerb is offline
 
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Prior post to check for debris in carb bowls makes sense.

Based on prior experience, you may want to check carb floats. They have had ongoing issues with absorbing fuel and gaining weight.

Also - carb balance.

I was in a friend's RV-12 when he had "sunken" carb floats and the behavior was pretty much identical to what you describe - so much so that takeoff was aborted.
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  #4  
Old 03-22-2018, 05:54 PM
DHeal DHeal is offline
 
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I've had many overweight floats in my RV-12. In my experience, overweight floats do not create much of an issue at high-power settings -- the engine runs fine. The high fuel flow at high-power settings seems to diminish the negative effect of heavy floats. If I get a whiff of fuel odor during the engine's operation or see fuel residue in the carb trays, I suspect heavy floats. In any event, its a good idea to check the floats' weights and do a carb balance.
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Last edited by DHeal : 03-22-2018 at 08:20 PM.
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  #5  
Old 03-22-2018, 06:36 PM
Mich48041 Mich48041 is offline
 
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The voltage regulator does not supply electrical power to the ULS engine.
Other possible causes of rough engine are an engine driven fuel pump going bad or using winter gasoline when it is very warm outside (vapor lock).
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  #6  
Old 03-22-2018, 06:42 PM
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Was the engine started from cold or was it warm(hot) from a previous flight?
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  #7  
Old 03-22-2018, 07:02 PM
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When was the last time you had the carbs serviced? Rotax recommends every 200 hours.
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  #8  
Old 03-22-2018, 07:20 PM
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tomkk tomkk is offline
 
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Quote:
Originally Posted by DHeal View Post
I've had many overweight floats in my RV-12. In my experience, overweight floats do not create much of an issue at high-power settings -- the engine runs fine. The high fuel fuel flow at high-power settings seems to diminish the negative effect of heavy floats. If I get a whiff of fuel odor during the engine's operation or see fuel residue in the carb trays, I suspect heavy floats. In any event, its a good idea to check the floats' weights and do a carb balance.
My first set of bad floats acted OP's symptoms ..
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  #9  
Old 03-23-2018, 09:18 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Bob,
Particularly since it sounds like the problem is intermittent, in all likelihood it is a carb. / fuel delivery related problem.

What you are seeing is a common symptom of a carb. with some contamination or an out of spec. float.
Contamination can be a problem to resolve because sometimes you can even make an entire flight and not have it act up, but then it does again on the next.
A float problem is easy to identify by just removing them and checking the weight.
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  #10  
Old 03-23-2018, 11:51 AM
bob1393 bob1393 is offline
 
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Thanks Scott and others for the reply. We have the new floats and did check them at 200 hours and they were fine. We did not check them again at 400 hours. We will check them now and the gascolator also to see if there is any debris or contamination as well as weigh the floats.

Bob
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