Engine fluctuation

[Marc Hardenberg]

Today we had an engine problem after t/o, when flying full throttle on down wind the engine rpm dropt from ~6150 to 5800 and was fluctuating between ~5800-5850, no warnings where present on the engine instrument.

We decided to retract the engine and land.

After the landing we did a visual inspection and could not find any thing, there after we did a test run on the ground, when going full throttle the rpm fluctuated between 4900 and 5150, again no warnings where present on the engine instrument. 

When switching to the redundancy system the fluctuation stopt and the rpm went up.

We checked the connector of the throttle valve sensor and put some contact spray on it, we than did another test run but the low rpm and fluctuation remained.

We visual checkt the rpm sensor and ignition valves but everything seems oke.

Any body a suggestion?

[Edoardo Jacucci]

Hi Marc

We had a similar problem.

The current hypothesis (we can validate it once we get the new spare part and try again) is related to the part in the picture below.

With temperature and dilatation, more air may pass through which impacts the performance of the engine causing it to reduce RPM.

This may be due to wear since this part is quite old in our Arcus.

Let us know what you think.

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Edoardo Jacucci

[Marc Hardenberg]

Hi Edoardo,

We have an Arcus M 20 (sn 257) with only 21hr run time on the engine that is not much in my opinion, tomorrow we intend to chance the wires of the throttle valve sensor to the second potentiometer, I wi keep you posted.

This is how it is now.

[Bill Tugnett]

Gentlemen, in January we had a similar problem with the butterfly shaft on the rear throttle body.  The shaft had become loose such that at WOT, the butterfly (Drosselklappe) was over extended by approx. 20 degrees, causing a 400 – 500 drop in rpm. Between the two throttle bodies, the rear shaft is attached to a semi circular steel disk & the shaft end has a male rectangular section which is pressed into a corresponding female section in the disk. Wear in the shaft at this point had caused it to become loose. Although the front throttle body appeared ok, we have returned both throttle bodies to SOLO for repair / reconditioning. Regards,  Bill   VH-FIG

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[Andreas]

As the trouble occurs with butterfly valve should in position allowing max air flow through even a little wear at the location you pointed at should be not an issue.
BR Andreas

[Daniel GUEDON]

On snr 202 we had the same kind of problem. 

We first had the shafts connection butterfly 1 to butterfly 2 issue fixed by SOLO, but it did not help much. 

Then we identified that the throttle sensor adjustment was unstable (full throttle sensor adjusted at 89.7 degrees as measured by Win Trijekt) due to some flexibility and freeplay in the link between the sensor and the throttle command butee on the butterfly shaft. The only way to get a stable full throttle rpm was to adjust the sensor at less than 88 degrees. Sensor replacement and attempts to reduce sensor connection to butterfly shaft freeplay (which we could make null) did not help. 

When the ground adjustment was above 89 degrees we noticed that vibrations and/or flexibility and /or freeplay (inside the sensor ?) were randomly taking the sensor above 90 degrees at full throttle, which, once the engine runs, causes the injection computer to provide bad command to the injectors, thus giving lower than full rpm, and random rpm drops. A couple of times we happened to have rpm drops up to 1000rpm.

At the end the only way to get a stable high (not full ) rpm value with no random drops was to adjust the sensor below 88 degrees, or 89.5 degrees and adjust the throttle command 1-2cm back from full. Which in both cases was giving us around 5900rpm

Then we decided to go for the Solo TM4600-9, which solved the problem.

Hope this helps

Daniel

[Marc Hardenberg]

Gentlemen,

On the way back from our vacation at Aosta we drove to Schempp-Hirth to fix the problem, the problem was a the cable on the first injection valve that was broken.

Quick fix everything works good again.

Best regards,

Marc

O

Op vrijdag 27 maart 2026 om 15:52:40 UTC+1 schreef daniel...@gmail.com: