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MileHighCTLS

MINOR LOSS OF SOME POWER - WHY?

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Just did my annual with no major issues. BUT upon my first flight afterwards, I noticed a minor loss of continual power. In other words, my Rotax 912ULS was simply not turning as fast and as powerful as it did just prior to the annual. As soon as I took off I noticed my climb-out was a bit flat. My top RPM (with full power) was around 4750 to 4780. I usually get above 4900rpm with full power and when I level off, I can easily exceed the 5000 rpm if I desired.

There were no major issues with the annual ... as I performed all of the following regarding the engine:

  • BTW ... total time: 180
  • Compression GREAT ...  79/80 all around
  • K&N air filter cleaned (with K&N kit)
  • Spark plugs cleaned and gapped to factory specs
  • Fuel flow test was perfect - both wings
  • Gascolator screen checked and cleaned - no debris or sediment found

If anything, I expected the engine to hum perfectly! But it seems to be a bit sluggish. Why oh why?

I seriously doubt there is a major problem because the engine runs so smoothly. There are no misses, no weird noises or any unusual vibrations.

There are two observations to consider but not sure if they mean anything. On my Dynon EGT digital gauges, two cylinders are monitored: #1 (left side of engine) and #2 (right side of engine).

OBSERVATION ONE:  #2 shows a slightly lower EGT, by around 100-degrees.

OBSERVATION TWO: I am using 91-octane, 10% ethanol blend, that is about a year old (but the plane flew just fine before annual)

I would appreciate any thoughts you may have!

Tom  

 

 

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I have had similar before, and carb heat was on with the knob in the off position. Once the nut seccuring the cable behind the airbox came loose. The second time was an issue behind the panel.

Also over application of the K&N red oil can restrict airflow. It is one of those things that takes way less than you think it should.

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Was the prop re-pitched?  If it was made over coarse your top RPM and climb out can be reduced.

Re-check your ignition system, make sure plug wires are all snug.  You'd see a problem on your mag check, but it can't hurt to check the wires.

Tom is right about the K&N...you could remove the filter and do a run up and see if your power comes back.  If so, just rinse the filter and reapply (much less this time) the oil.

Tom, I see almost no discernible RPM difference between carb heat on and off (yes, I confirmed the door was working 😁 )...is the LS considerably different? 

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Yes the LS is different than the CTSW. It actually runs a duct to the heat shroud on the muffler. It may only show a drop of 50 RPM on run up, but the loss in power is more noticeable at takeoff power

After re-reading the original post I would definitely get rid of the old fuel and replace with new, or at a minimum add an equal amount of 100LL. With auto fuel that old it could lead to detonation, and that will be costly. I don't think this is your issue, but I would hate to see you ruin an engine.

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50 minutes ago, Tom Baker said:

After re-reading the original post I would definitely get rid of the old fuel and replace with new, or at a minimum add an equal amount of 100LL. With auto fuel that old it could lead to detonation, and that will be costly. I don't think this is your issue, but I would hate to see you ruin an engine.

I missed that too!  Yeah a year is a long time for ethanol fuel.  I've used ethanol gas up to 3 months old, but I don't think I'd go much longer than that.   The good news is you can drain it an put it in your car, go-kart, lawnmower, or chainsaw.  :D

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The linkage on the backside of the air chamber has a very delicate spring that can keep the flapper from closing all the way. I agree with Tom, reduced take off power sounds like a carb heat issue.

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30 minutes ago, Tip said:

The linkage on the backside of the air chamber has a very delicate spring that can keep the flapper from closing all the way. I agree with Tom, reduced take off power sounds like a carb heat issue.

"air chamber"? Location?

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14 minutes ago, MileHighCTLS said:

"air chamber"? Location?

Air box that is connected to the carbs. The carb heat valve connections are on the back side. There are 2 valves that are connected when you pull the carb heat control you close the valve to the filtered air and open the valve to the heated air. There is a spring to aid in over center when turning carb heat off.

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Fuel is worth a try. My 1991 Stealth Twin Turbo started running poorly and I start thinking big money and parts that are expensive if you can find them. Should have bought the 1991 Corvette instead.:fainting-1344:Anyway, premium with ethanol was put in in early October and the tank was nearly empty. Filled it with fresh premium and after a few miles the problem went away. Probably would not have had the problem if I had treated it with Stabil back in Oct.

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I would agree with Tom on this one, I had the carb heat return spring on one of our CTLS's break allowing the carb heat to stay on when the knob was in.  Noticeable reduced performance in climb and cruise and slightly worse ignition check and offset EGT values.

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What's really weird is that cylinder #1 is on the left side and cylinder #2 is on the right.

That suggests the engine is mounted up-side-down.

Mike Koerner

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7 hours ago, Mike Koerner said:

What's really weird is that cylinder #1 is on the left side and cylinder #2 is on the right.

That suggests the engine is mounted up-side-down.

Mike Koerner

As a dry sump boxer-style engine, is there really a "right side up"?  I guess wherever the carbs are placed is the "top" given that configuration...

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9 hours ago, Mike Koerner said:

What's really weird is that cylinder #1 is on the left side and cylinder #2 is on the right.

That suggests the engine is mounted up-side-down.

Mike Koerner

You need a smiley face in there. For those like me who are left right challenged it is easy to make a mistake like that. Years ago when I was doing my private pilot checkride the examiner ask for a steep turn to the right. I was about half way through the turn before I realized I was going to the left. I said, "as soon as I finish this one to the left I will do one to the right". 

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1 minute ago, Tom Baker said:

You need a smiley face in there. For those like me who are left right challenged it is easy to make a mistake like that. Years ago when I was doing my private pilot checkride the examiner ask for a steep turn to the right. I was about half way through the turn before I realized I was going to the left. I said, "as soon as I finish this one to the left I will do one to the right". 

Glad I'm not the only one.  I learned left/right late as a child, and I still have to think a second about it.  I also have said "on your three o'clock...oops, I mean nine o'clock" more times than I want to admit.  😏

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1 hour ago, FlyingMonkey said:

Glad I'm not the only one.  I learned left/right late as a child, and I still have to think a second about it.  I also have said "on your three o'clock...oops, I mean nine o'clock" more times than I want to admit.  😏

The three o'clock nine o'clock is understandable if you are calling your position for someone else, because you have to picture yourself in their position. 

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Be sure to double-check the little black hose that connects to the side of the carb. If it comes off you will not be able to get full power. If both are still on you might want to check for a leak at the connection. It acts like you are running with carb heat on and sometimes runs a little rough When it is off.

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back in 2012 I had power loss, at full throttle. Turned out to be defective carb floats, some pieces came off and got into main jet. Since then many revisions of floats (and part numbers ) have happened. I didn’t see your checking of float bowls in the diagnosis. may be worth looking.

 

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I once had a similar issue with the 912ULS in my AeroTrek. I was advised that it could be poor-quality fuel (I was using 91 E10). Drained it out, refilled with fuel from a different station, and it perked right up. No problems since. As an added layer of ensuring clean fuel, I started filtering through a Mr. Funnel. Don't know if it's really making a difference, other than the placebo effect. 

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