Sport Pilot Talk

I have an 2006 Evektor Sportstar with a Rotax 912 ULS. Both aircraft and engine have 1850 hours on the clock.

Today I was on a 45 minute flight from KLHZ to KBUY (Burlington, NC). I was cruising at 2800 ft MSL and 90 kts (5,000 RPM). After making my 10 mile call when approaching Burlington at maybe 7 or 8 miles out I reduced power slightly but immediately afterward the engine continued to lose power over a period of maybe 20 seconds. I switched fuel tanks and turned on the electric fuel pump. Both tanks had plenty of fuel. I checked temperatures and fuel and oil pressure. They all looked good. The engine was running but creating very little power. I was at full throttle and 60 kts and could only get 3750 RPM out of the engine. This was not quite enough to maintain altitude. I declared an emergency over the KBUY CTAF and stated my intention to enter a left base for runway 24 from directly east of the field. I did just that and landed without incident.

Immediately after I landed and I taxied off of the runway I was able to run the engine up to 5,000 RPM. I parked and removed the cowl and nothing looked out of place. I checked the fuel sumps for water and found nothing (I had checked them before the flight as well). Fuel levels were at 9 gals left and 7 gals right.

I had a momentary partial loss of power about 6 weeks and 5 flight hours ago that in hindsight might be the same issue. This case was also midflight but the power was only reduced for 2 or 3 seconds. In this case I grabbed the fuel selector and twisted it and noted that it was not fully switched to the right-hand tank. It was not in the detent. When I moved the selector a small amount into the detent that is when full power returned. Perhaps this was only coincidental.

I badly need to get this sorted out before I fly again. Any thoughts?

In my case it was a bit of debris in one of the carbs - very similar symptoms except it happened on the takeoff roll.
This sort of problem can manifest itself in a semi random fashion, depending if that piece of debris ends up blocking the fuel jet in the carburetor while it freely floats in the bowl ...

https://youtu.be/PCmdNnOrXOc

Dave, were you flying with MOGAS or 100LL? Could have been CARB ICE. Does your bird’s ROTAX have the carb ice feature built in? That’s a constant flow of coolant thru the carbs. I have that set up in the Sling. And, do you have a return line? Not saying that’s the problem, just one more place to check.

I agree with warmi - our BING carburetors are mechanical wonders, but seemingly very vulnerable to any debris finding its way to their float bowls, and from there partially or totally blocking their main jets. When that occurs on one side, it can lead to a 50% power loss and LOTS of vibration. I’ve had it happen twice. I’ve heard that barbed fitting can shave tiny bits of rubber from fuel lines, so that’s something to be aware of.

On BMW motorcycles, which use essentially the same BING’s, it’s pretty common to fit a small inline filter right at the carb inlet. I’m sort of surprised our engines don’t utilize something similar.

Debris in the carb will normally make it run rough, and he didn't mention it running rough just a loss of power. Depending on the time of day and temperature carb ice could have been a possibility. Also do you have the soft start ignition modules?

During the loss of power it was running rough, very rough. The panel was a blurr with all the vibration.

3Dreaming wrote:Debris in the carb will normally make it run rough, and he didn't mention it running rough just a loss of power. Depending on the time of day and temperature carb ice could have been a possibility. Also do you have the soft start ignition modules?

I would expect that as well since we are talking here about unbalanced output from two carburetors but look at my video - there was no roughness whatsoever , just loss of power very similar to simply pulling back on the throttle.

Btw. I forgot to mention that before my very obvious power reduction during take off, I had what I thought was power reduction during flight a day before.It seemed like my throttled backed out on its own ( just based on engine noise ) so I kind of worked it a bit back and forth without thinking much and then everything went back to normal - i thought maybe I bumped it myself a bit or something but in retrospect it must have been the same problem. One lesson for myself out of this was, when you think something is wrong but you can’t quite put your finger on it , don’t dismiss it , have it checked out.

Sling 2 Pilot wrote:Dave, were you flying with MOGAS or 100LL? Could have been CARB ICE. Does your bird’s ROTAX have the carb ice feature built in? That’s a constant flow of coolant thru the carbs. I have that set up in the Sling. And, do you have a return line? Not saying that’s the problem, just one more place to check.

At the time I was running a mix of MOGAS and 100LL. I almost always run MOGAS but I just had 10 gals of 100LL added before the flight. I don't know if I have the carb ice feature that you mention. What is the return line? If I had coolant flowing through the carb wouldn't it have to have a return line?

I do have carb heat in the plane but I didn't try it. I lost power only a couple seconds after reducing power from cruise power to maybe half power. Maybe I should have tried carb heat but I didn't think that it was in any way a situation that demanded it. I did try closing the throttle and opening it a couple times. I did have good throttle control of the little power that remained

Dave:
Check the carb bowls for possible debris just to eliminate this possibility - it is pretty simple.

Here is a video on how to do it.
https://youtu.be/XBT-yQ_X3N8

3Dreaming wrote:Debris in the carb will normally make it run rough, and he didn't mention it running rough just a loss of power. Depending on the time of day and temperature carb ice could have been a possibility. Also do you have the soft start ignition modules?

It was rough. To answer your other questions it was about 6:15 pm and about 70 deg F. The ignition modules on top of the engine ( part # 965444) were installed new in Feb 2018. The logs list the old part # as 966726.

Warmi wrote:In my case it was a bit of debris in one of the carbs - very similar symptoms except it happened on the takeoff roll.
This sort of problem can manifest itself in a semi random fashion, depending if that piece of debris ends up blocking the fuel jet in the carburetor while it freely floats in the bowl ...

https://youtu.be/PCmdNnOrXOc

You are very lucky it didn't happen a few moments later when you were climbing past the end of the runway! I am lucky I had some altitude to work with

Dave C wrote:

3Dreaming wrote:Debris in the carb will normally make it run rough, and he didn't mention it running rough just a loss of power. Depending on the time of day and temperature carb ice could have been a possibility. Also do you have the soft start ignition modules?

It was rough. To answer your other questions it was about 6:15 pm and about 70 deg F. The ignition modules on top of the engine ( part # 965444) were installed new in Feb 2018. The logs list the old part # as 966726.

If it was rough I would suspect carb ice or debris in the float bowl. as the first 2 culprits. One other thing is a sticking piston in the carb.

I'm leaning toward carb ice. That engine is most vulnerable to carb icing at 70 F or above, with relative humidity up around 60% or higher. The SportStar's carb heat circuit works well, as long as you realize that the engine will lose more power at first when you pull it. It has to get worse before it can get better!

drseti wrote:I'm leaning toward carb ice. That engine is most vulnerable to carb icing at 70 F or above, with relative humidity up around 60% or higher. The SportStar's carb heat circuit works well, as long as you realize that the engine will lose more power at first when you pull it. It has to get worse before it can get better!

I looked back at the reported weather from yesterday. At 6 pm on the ground in Burlington it was 81 F and 42% humidity

That temp sounds about right for carb ice. Humidity a bit low, but not out of the question.

Here's a link to a carb ice probability graph:

http://avsport.org/docs/carb_icing.pdf

Looks like these conditions equate to the "moderate icing, cruise power; serious icing, descent power" zone.