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RPM drop with a 914 above 100%

  • Jacques De Jonghe
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5 years 3 months ago - 5 years 3 months ago #3629 by Jacques De Jonghe
Jacques De Jonghe created the topic: RPM drop with a 914 above 100%
Hello all,

Recently, I had to abort a take off with my Europa 914 airmaster due to the fact that I was facing an RPM drop above 100%. The ROTAX has less than 330 hours.


I already looked at the following items:
- replaced the fuel with fresh one
- fuel pressure is OK
- TCU - transfer function according to heavy maintenance manual and solenoid gets 12V above 108%, so should be OK
- turbo wastegate fully closes
- air filter cleaned up

The issue is still present and my next step is to look at the carbs (membranes have been replaced less than 200 hours ago). Any other ideas? Where should I specifically need to look at the carbs?

The attached file from the TCU log depicts the issue starting from line 989.

Thanks for relevant input.

Jacques

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Last Edit: 5 years 3 months ago by Jacques De Jonghe. Reason: typo

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5 years 3 months ago #3630 by Jeff Nelson
Jeff Nelson replied the topic: Re: RPM drop with a 914 above 100%
I will be watching your post with great interest since I am having a similar problem. At full power, the rpm will not rise above a similar 5100- 5150 rpm range. I just overhauled and balanced the carburetors with no effect. I found nothing in the carbs. I just ordered the parts to check the fuel regulator pressure but the indicator light that would indicate a very low fuel pressure is not triggering (at less than 0.1 bar).

Fuel and air filters have been cleaned, fuel changed. Boost goes up to redline manifold pressure. The 914 has about 220 hours on it.

The rpm will increase to max rpm in cruise when the airspeed takes the load off the prop. I will check the tack next but with it indicating, consistently, full rpm at higher airspeeds, I doubt it is the problem.

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5 years 3 months ago #3631 by Roger Lee
Roger Lee replied the topic: Re: RPM drop with a 914 above 100%
Fill these out and send them in. There is several people having a similar issue.

CSIR report

www.rotax-owner.com/support/sir-service-information-report

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
The following user(s) said Thank You: Rupert Gruen

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5 years 3 months ago #3632 by Roger Lee
Roger Lee replied the topic: Re: RPM drop with a 914 above 100%
A helpful comment from a friend,

This is a good idea for any new 912 or 914 user. It's very good advice to head.
"Just a heads up...I have investigated more than one crash over the years of reasonably new aircraft with 914 engines. Most used fibreglass tanks and the finger screen filters were plugged almost off. Its a common problem if they do not clean them or check them. New fuel tanks give up a huge amount of fine hairs from the glass. Sometimes tanks made that use sealing compounds also send debris into the fuel line and its all over for the pump after that. The builder needs to plan for filter checks frequently during the first 100 hours. (not just the gascolator screen)"

I too have seen many a screen and or fuel filter with lots of fine hairs from the tanks. Just take a look for a while to play it safe.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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5 years 3 months ago #3634 by Jeff Nelson
Jeff Nelson replied the topic: Re: RPM drop with a 914 above 100%
Roger:

Thanks. All suggestions are welcome. In my case, the fuel tank is stainless steel and I have found nothing significant in the fuel filter.

It seems like I am going through one of those phases where I have nagging obscure problems. I've got problems with another toy - the instrument vacuum system reads low when it is cold in the cockpit. After lots of very hard to access hose replacement and annoying troubleshooting, it turns out the vacuum gauge itself has a small leak and it reads low when it is cold. I also have an intermittant problem with a fuel gauge - fine on the ground but erratic in flight. Probably a typical ground problem in a sensitive capacitance system but I have not been able to find it yet.

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4 years 7 months ago #5125 by Carlos Chazarra
Carlos Chazarra replied the topic: Re: RPM drop with a 914 above 100%
Roger,
I have exactly the same problem with a giro Ela 07 with 914: at WOT , stopped, only I have 4500 Rpm. Then, it colapses to 4000 rpm, by itself, failing.
So, Last TO was aborted cause not enough power to climb.
Checked and replaced by brand news:
-fuel
-fuel filter
-fuel pipes and vent pipes, all checked.
-pre filters of fuel pumps.
-gascolator
-air filter
-fuel distribuiitor. All inside checked, and menbrane.
-carb cups.
-sparks. New ones.

Still only 4500 Rpm dropping to 4000 at 100% power, airfield.
Any idea anybody to continue ?
I am lost.

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  • Jacques De Jonghe
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4 years 7 months ago #5126 by Jacques De Jonghe
Jacques De Jonghe replied the topic: Re: RPM drop with a 914 above 100%
Carlos, I found the following issues during the debug of this problem:
- Debris were located in the hoses before the fuel pumps due to a hole in the gascolator grid
- The rubber between the manifold and the carbs were not hermetic, so I replaced them
- The carbs were replaced - not willing to wait for the older ones to be overhauled

That solved my issues.

Jacques

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4 years 7 months ago #5128 by Roger Lee
Roger Lee replied the topic: RPM drop with a 914 above 100%
If you believe it is a full issue and you have found debris and cleaned it, but still have an issue then the whole fuel system may need to be cleaned.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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4 years 7 months ago #5129 by Carlos Chazarra
Carlos Chazarra replied the topic: Re: RPM drop with a 914 above 100%
Thanks for the answer,
Well, fuel filters and gascolator were checked.
In fact the gyro is new, with 250 hours total time since new, with the 914 as well new.
All OK from factory, never a problem.
I am worried because the the trouble I have, with the loosing of 1500 rpm at 100% power, sea level, it is always there, in all tests I do.
At 100 % power I have only 4500 rpm, but the main point is that always it collapses in the same point and drop to 4000 revs. Is not randomly failing and not, it fails always.
I realized the problem last flight, low power at take off, but I could manage to level and fly back and land.
Since then, months ago, just couple of aborted take offs, and 7 hours of land engine checkings without success. I have a private short airfield, close to Mediterranean Sea, and....well, with 4000 Rpm, ...no way to climb.
Even the turbo, I don't really know if it should go on or not...

I will go over carbs, again.

Thanks for helpful ideas.

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4 years 7 months ago #5135 by Karl Kistler
Karl Kistler replied the topic: Re: RPM drop with a 914 above 100%
I would disconnect the fuelline from carburator and check the quantity of fuelflow you have with 1 fuelpump running. As you know, the r914 needs maximum about 33 l/h with full power, you should have about 80 l/h to be on the save side.
Karl

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4 years 7 months ago #5136 by Carlos Chazarra
Carlos Chazarra replied the topic: Re: RPM drop with a 914 above 100%
Hi Karl,
Disconnect metallic pipe coming to every carb, and measure fuel flow in each pipe, switching on fuel pump?
Is this what you propose ?
So, you think can be one fuel pump not working well?
Thank

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4 years 7 months ago #5137 by Karl Kistler
Karl Kistler replied the topic: Re: RPM drop with a 914 above 100%
No, just disconnect the fuelfeed line into the fuel pressure regulator to permit the fuelflow check. This gives you the chance to check, if you have enough fuel flow for the engine. (Check figure 73-3 in R914 maintenance manual)

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4 years 7 months ago #5138 by Karl Kistler
Karl Kistler replied the topic: Re: RPM drop with a 914 above 100%
To have a clue, what results you shoult have, see the following results on my r914:
Battery voltage 12.5V: 2.11 l/min (126l/h)
Battery 13.3V: 2.57 l/min (155 l/h);
The engine needs 0.55 l/min (33l/h)

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4 years 7 months ago #5142 by Roger Lee
Roger Lee replied the topic: RPM drop with a 914 above 100%
Hi Carlos,

Once you eliminate a fuel delivery issue then it's time to think about electrical, sensors, turbo.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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4 years 7 months ago #5144 by Carlos Chazarra
Carlos Chazarra replied the topic: RPM drop with a 914 above 100%
Thanks to all,
Interesting.
A clue... Today I did again test at full power: when it was, as always, in the range of 4500 rpm, 34" map, it fails down to 4000. With all throttle ahead, and the problem arising with rpm, I cut suddenly magnetos and fuel pumps, in order to open carbs just in that position of breakdown.
Well, I open carbs hubs and I find
15 cc fuel right carb
29 cc fuel left carb

Useful info?

I know this is not a good procedure for engine, but I have to have a clue...

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4 years 7 months ago #5146 by Karl Kistler
Karl Kistler replied the topic: RPM drop with a 914 above 100%
This is a sign, that you have a fuel problem, perform the Fuelfllow check as imentioned above

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4 years 7 months ago #5149 by Roger Lee
Roger Lee replied the topic: RPM drop with a 914 above 100%
Sounds like you may still have a fuel delivery issue.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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4 years 7 months ago #5156 by Rob Seaton
Rob Seaton replied the topic: RPM drop with a 914 above 100%
May be the float bowls gasket is allowing boost pressure to escape? Even if you have no fuel stains around the bowl it can happen. Make sure the bowl is not distorted by over-torquing the bolt and the sealing surface is true. Pre-soaking the gasket helps (thanks to Lockwood for that tip)
The following user(s) said Thank You: Carlos Chazarra

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4 years 7 months ago #5169 by Carlos Chazarra
Carlos Chazarra replied the topic: RPM drop with a 914 above 100%
Karl, fuelflow is checked as you say, and it is ok. Thanks for the tip.
Rob,....., I saw right crab tray with some kind of leak of fuel, seen some small drop of fuel coming out from the gasket..... And couple of flights ago, some brown colour ( As from fuel) in the other side of that carb, facing to crankshaft.
Check that and replaced for new, and say to you.!

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4 years 7 months ago #5179 by Carlos Chazarra
Carlos Chazarra replied the topic: RPM drop with a 914 above 100%
Today I carried out, again, full power tests, once I have checked and cleaned all fuel pipes, distributor, pipes to carbs, carb bowls, floats, jets, pins, and ....still exactly same problem: no more than 4500 rpm and drop to 4000.
I have checked, one more time, in that position, the level of fuel inside bowls, more precisely, and the difference between left and right is surprising: 40 cc left, 19 cc right.
I observe as well a slight leak of fuel from rear part of the right carb, probably coming from the gasket, not much, but is dry in the other carb.
It, then, seems to be fuel delivery issue, as Roger says, in the right carb, with possibly a lost of boost or fuel in it, (as Rob tells).

Is possible that, if this is the matter, it causes so much drop in t he powerful of a Rotax 914 from 5.500 to 4000 rpm.??
Anybody have seen a case like this?

I will have the carbs overhauled, I think.

Thanks

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