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  #1  
Old 12-18-2017, 07:50 PM
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scottmillhouse scottmillhouse is offline
 
Join Date: Apr 2007
Location: Madison, AL
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Default In flight Rotax power loss

First this is kind of long. Background: Rotax 912 ULS over 200 hours. A few hours after annual. On annual new plugs and the floats replaced on left carb. One float was heavy. Carbs were balanced before I found out float was heavy so they now appear to be a little off balance. Prop pitched a little coarser than before, testing the denser winter air with static around 5000 on ground and about 5100 in climb out. Flown about 5 hours in the latest configuration. Climb solo at around 1400 fpm today.

After take off climbed to 3000' and ran a few minutes at 5500 rpm at 124 KTS TAS. Slowed to 5350 for cruise and shortly after stabilized rpm suddenly dropped to 4700 and felt a little rough. Full throttle application caused no power increase. Reducing power the engine was much rougher. I turned around and limped along back home until the Dynon showed well within glide distance. I then stopped the prop and requested traffic clearance for a dead stick landing. In retrospect I should have kept the engine at WOT since it was relatively smooth there and not reduced power and shut it off until in the pattern but I was afraid whatever was wrong would be made worse. With prop stopped and holding 60 knots until touch down I averaged 600 fpm descent rate. I now know stopped engine glide performance.

On ground the engine started fine with normal engine run up. Powering up the engine felt starved and would not go over 4600 rpm and would shutter and run rougher the more throttle you added to increase rpm. Pulled plugs and if anything they looked lean with slight light gray deposits. Compression felt fine but I will run a compression check. Gasolator clear, everything in the green and as before except the in flight EGT difference.

Downloaded Dynon. It showed all in line up to about 1/2 way in my 5500 rpm run when the right and left EGT deviated from 712 and 700 to 726 and 793. That spread continued until I shut down the engine. Before I lost power fuel flow was 5.1 gph and it then deviated from 4.4 to 5.1.

I'm thinking a fuel line obstruction after the totalizer but before carbs so after the compression check I'll start disconnecting lines and checking fuel flow. Other idea is an ignition breakdown at rpm or under load. Hopefully nothing internal.

Ideas?

Before I start another s... storm on 5100 rpm in climb as I see being heavily discussed, that is at 75 kts climb which is only maintained for a short time. Cruise climb is well over 5200 rpm with rate of climb decreasing accordingly. Yes I'm pitched currently as a trial to exceed 120 kts but not at sea level or full gross weight but 3000' solo. It will even gain another knot or two when you run it up to red line.
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RV-12 #120515, N319RV 1st flight 12/2015 now over 270 hours.
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Last edited by scottmillhouse : 12-18-2017 at 08:15 PM. Reason: added text
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Old 12-18-2017, 08:19 PM
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Special Delivery Special Delivery is offline
 
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Classic symptom of trash in a carb. Pull em, clean em, and $1 to a doughnut your problem will be solved.
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Old 12-18-2017, 08:27 PM
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scottmillhouse scottmillhouse is offline
 
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Could be but unlikely in a carb since I have two carbs and both sides appear to have lost power at the same time. (my logic was wrong, only the left carb was effected and that pulled the right side down and total power) At annual I replaced gasolator screen only because I damaged it upon removal for inspection. Zero deposits on screen or in bowl with 200 hours and two years.
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Got medical back, now building a 7A; N579RV reserved, new engine installed, doing FWF, instruments & finish painting.
RV-12 #120515, N319RV 1st flight 12/2015 now over 270 hours.
RV-9A, 536 hours sold, RV-7 sold, Kitfox sold

Last edited by scottmillhouse : 01-04-2018 at 12:59 PM. Reason: added note
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Old 12-18-2017, 08:52 PM
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Special Delivery Special Delivery is offline
 
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Please report back when you find the problem.
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Last edited by Special Delivery : 12-19-2017 at 04:42 AM.
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  #5  
Old 12-18-2017, 09:04 PM
Azjulian Azjulian is offline
 
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what's the fuel pressure at WOT ? If you aren't showing low then I would check carbs

are you getting full unobstructed range of movement on the throttle on both carbs ?

I would check there is no fuel leaking out of the bodies and do a reset of mechanical and pneumatic sync before anything else

any cracks in the rubber throat attachment to the inlet manifold ?
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Old 12-18-2017, 10:06 PM
RFSchaller RFSchaller is offline
 
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Have you pulled the cowling yet? I had a carburetor work itís way loose about 5 Hours after reinstalling when it didnít seat properly in the socket. I had some similar symptoms.
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Old 12-18-2017, 10:32 PM
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scottmillhouse scottmillhouse is offline
 
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Default answers

Fuel pressure over 5 psi, normal range, full throttle travel, choke not on, did remove cowl and all looked good including carb sockets, no fuel dripping or anything looking out of place. 93 octane auto fuel with ethanol about 3 weeks old, plane was not flown for two weeks, OAT about 50-55 on ground. 4 degree dew point spread but had same problem an hour later after under cowl inspection so not carb ice.
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Scott- 2018 dues paid
Got medical back, now building a 7A; N579RV reserved, new engine installed, doing FWF, instruments & finish painting.
RV-12 #120515, N319RV 1st flight 12/2015 now over 270 hours.
RV-9A, 536 hours sold, RV-7 sold, Kitfox sold
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Old 12-18-2017, 11:51 PM
Driftdown Driftdown is offline
 
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Those are classic symptoms.
Check the obvious first.
Drop the carb bowls and check for debris at the bottom of the bowls. As you remove each bowl (instructional video on uTube) be careful not to spill/empty out the bowls, so you get a good read, on any foreign objects, submerged or floating around.
I bet debris is clogging one or both of the jets.
It only takes a tiny speck, to cause a rough running engine.

Last edited by Driftdown : 12-18-2017 at 11:56 PM.
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Old 12-19-2017, 05:54 AM
BigJohn BigJohn is offline
 
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Quote:
Originally Posted by scottmillhouse View Post
Could be but unlikely in a carb since I have two carbs and both sides appear to have lost power at the same time...........
I canít quite figure out the above conclusion, since you reported in your original post quite a large difference in EGT berween sides when the loss of power occurred. That indicated to me a difference in mixture between sides, and therefore a difference in power generated, which would explain the roughness. IMHO it is likely one of your carbs has a blockage.
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  #10  
Old 12-19-2017, 07:56 AM
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DanH DanH is offline
 
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In addition to a trash check in the float bowls, note that Bings can be blocked with a flake of trash in the fuel inlet, upstream of the float needle.
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