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914 RPM problems

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5 months 2 weeks ago - 5 months 2 weeks ago #16078 by jetandgyro
jetandgyro created the topic: 914 RPM problems
Hi all, hope someone can help.

First I had a electrical failure and I lost my fuel pumps. I made a forced landing...no damage...

After fixing this problem I flew and got problems with my RPM. Always changing between 4800 and 5100 RPM.

Maintenance did a great job and cleaned all carburators and did a complete check (100h). Flew Gyrocopter home...no problems. Today, one day later i flew 4 patterns. First and second no problems.
At the 3rd after takeoff I had a blinking orang boost light for 2 seconds. I reduced power and continued. While changing thrust I had the feeling the power did not change very responsive. It always had a lack between moving throttle and changing of power. Same feeling on the 4th pattern although I am very alerted at the moment and probably a bit over reacting.

At the ground I advanced throttle to full power and reduced to 4900 RPM. No problem at all.

Has anybody an idea what could be the reason? Or where I should start to look?
Last Edit: 5 months 2 weeks ago by jetandgyro.

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5 months 2 weeks ago #16081 by Roger Lee
Roger Lee replied the topic: 914 RPM problems
Possibly some air in the system working its way through?

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 months 2 weeks ago - 5 months 2 weeks ago #16083 by jetandgyro
jetandgyro replied the topic: 914 RPM problems
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Last Edit: 5 months 2 weeks ago by jetandgyro.

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5 months 2 weeks ago #16086 by jetandgyro
jetandgyro replied the topic: 914 RPM problems
Hi Roger,

Which air are you talking about? Do you think it might be the fuel? The day I flew was very hot, 32 deg Celsius.
Also due to my very short patterns I prob. asked a lot of power from my Rotax.

Hope for some infos. :-)

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5 months 2 weeks ago #16087 by Roger Lee
Roger Lee replied the topic: 914 RPM problems
32c or 80F isn't hot. Hot is 100+F or 39c+.
Since carbs and the fuel system where taken apart possibly air was introduced into the system. It should be self clearing though. You may want to try flying again. Watch your temps t see how warm the engine is getting.

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 months 2 weeks ago #16095 by spiros economou
spiros economou replied the topic: 914 RPM problems
I have the exact same issue on my 914. When I change throttle setting let's say in a go around situation, the engine is not as responsive as it should. MAP is not increasing according to throttle position and RPM. It is slowly reaching it target pressure. During take off all is ok, full turbo boost and correct RPM. While on air I face this issue.

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4 months 2 weeks ago #16332 by James Elder
James Elder replied the topic: 914 RPM problems
Similar issue on our 914-based gyro. Just started recently. Engine would suddenly surge in flight (usually around 30" manifold pressure). Adjusted waste gate as per Rotax video and we haven't seen the in-flight surge since but now on full power, the engine will suddenly surge up to 40" and you need to cut the throttle quickly. Any ideas?

Thx.

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4 months 2 weeks ago #16334 by Rob Seaton
Rob Seaton replied the topic: 914 RPM problems
You should check or calibrate your throttle position. You may be operating in the nasty 100%-115% zone so the TCU thinks you want take off power and can be unstable if you do not move smoothly/quickly from 100% to 115%
Read "Understanding the 914"
www.rotax-owner.com/en/support-topmenu/t...anding-the-rotax-914

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4 months 2 weeks ago #16335 by James Elder
James Elder replied the topic: 914 RPM problems
Thanks - we tried that. Adjusted the wastegate per the Rotax procedure and recalibrated the throttle. But it didn't help and anyway I don't think it's that, as when it surges, it goes over the normal 38" turbo max.

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4 months 2 weeks ago #16341 by Rob Seaton
Rob Seaton replied the topic: 914 RPM problems
Sounds like you fixed the problem with the wastegate adjustment but now have a different issue. But what you describe is normal; you should go over 40" at full throttle (see overshoot note in the Operators manual P 2-2). After a few seconds it should settle back down to 40" (OK, 39.9 but who looks that close?)

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4 months 3 days ago #16447 by Michael Burton
Michael Burton replied the topic: 914 RPM problems
slow increase in turbo could show a need to lubricate /clean the wast gate bearing. It would also be a factor in turbo over shoot and map instability.

Things that can lead to this problem include

bad floats
leak at the float bowl
low fuel pressure
leak in the vacuum lines
bad connection to one of the sensors
corrosion on a sensor connection
plugged map sensor
servo cable kinked or corroded ( too much drag)
bad ground to the engine

The throttle setting above 35 inches is very fast and not usually set to some power other than 40' so yes it will be very fast from 35 to 40. this is a normal condition.

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1 month 1 day ago - 1 month 1 day ago #17288 by jetandgyro
jetandgyro replied the topic: 914 RPM problems
So here I am back with the same problem. After having a 100h check a few weeks ago we discovered that the reason for my rpm-surge (+-200 rpm) was dirty carburators. After having everything done i flew home (1 hour flight from maintenance) and the engine felt like an electric engine. Very smooth.
In the last few weeks I had a total flight time of 5 hours, always flights 20-30 min.

Yesterday I took the Gyro for a 1,5 hours flight and after appr. 1 hour the engine surges started again. In 2 seconds from 4900 rpm up to 5200 and back again. The whole rest of the flight (20 min). I decided to fly back to my maintenance guy.

Has anybody an idea what reason it could be? At the last 100 h check everything was done very thoroughly and they did spend many hours to find the reason.
The new idea is that maybe the fuel-line after the filters which goes to the 914 might be in a bad condition and thats why the carburators got dirty.

With an engine like this I don't want to fly anymore, I had my forced landing with the Gyro already this year!
Last Edit: 1 month 1 day ago by jetandgyro.

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1 month 1 day ago #17296 by Rob Seaton
Rob Seaton replied the topic: 914 RPM problems
You have to find the source of the contamination, if you suspect the fuel supply hoses are breaking down they will all need to be replaced with hose that can tolerate ethanol/avgas/mogas.
And then the whole system will need to be cleaned again.

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1 month 1 day ago #17305 by Roger Lee
Roger Lee replied the topic: 914 RPM problems
If carbs were dirty and the problem you may have cleaned the carbs, but still have debris floating to the carbs. Common causes are fuel hose was just changed and it wasn't done sterile enough, fuel hose clamps too tight and the hose has been cut inside and debris floating downstream, old hoses starting to breakdown.

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 weeks 1 day ago #17336 by Michael Burton
Michael Burton replied the topic: 914 RPM problems
Check all the o rings in the carb. If they leak then the carb will not hold pressure or it will suck air from the wrong place. This may cause the float bowls to empty and then refill causing the surge. You may also want to check the screens on the fuel pumps. If they are restricted it can cause the same issue. I would also check the vacuum lines that connect to the pressure regulator. If they are cracked or leaking it will have a similar effect.

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