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Hello,

 

I tried to find a similar topic but to no avail so here I go :

 

I own a pipistrel virus sw 121, fitted with a 912S3. This is an EASA CS-LSA certified aircraft, so I can't tweak it much myself, just in case. The EIS is integrated in the Garmin G3X.

 

There was something bothering since the beginning, but I couldn't really frame it : I was following the aircraft POH for startup: full choke, start, close choke while keeping RPM in the 2300-2400 range with throttle.

And then at some point, say 1 to 2 minutes in, the RPMs would increase by roughly 110. So if I was in the low 2400's, i'd have to reduce throttle a bit to stay below the 2500 RPM threshold.

Now it's a bit colder, and I noticed during startup that the EGT for cylinder #2 lagged behind (EGTs were 548-423-523-544°C 1 minute after closing the throttle). And the engine was running a bit rough, with a low frequency noise. Then 1 minute later, the RPMs would increase, the vibrations would stop, and the EGT for cylinder #2 catch up then exceed the other EGTs and stabilize 50°C higher than the others.

 

A mag check showed no significant difference between Left and Right, before or after the RPM increase. In flight, the EGT for cylinder #2 has been consistently 40-50°C higher than on the other cylinders.

 

Have you encountered this kind of behavior ? Should I worry ?

 

Thanks,

 

Nick.

 

  • Re: 912S3 strange cylinder #2 behavior

    by » 5 weeks ago


    I suggest check 2&4 side carburetor that give incorrect air fuel mixture.less or incorrect fuel cause higher EGT and also seet the engine, trash in the jets or float valve can cause the carb to run lean, raising the EGT.


  • Re: 912S3 strange cylinder #2 behavior

    by » 5 weeks ago


    How many hours on the engine. My engine also picks up in rpm and smoothness as it warms up. Is each EGT probe the same distance from the exhaust port (there is approximately a 100 deg temp drop each inch from port). Exhaust probes have a life, they wear out  and not all at the same rate. Also check resistance of the high voltage ignition wires from the top front left to right from cap to cap it should read about 15 K ohms, this can cause intermittent rough running. Do the same for the top back and the the bottom plug wire components. If it reads high or open circuit you can clip about 1/4" from the plug wire ends at the caps and reinstall with dielectric grease. Sometimes when doing maintenance/changing spark plugs the plug wires can get pulled slightly out of the plug cap. Easily found with a resistance check.

     

    https://441py33rout1ptjxn2lupv31-wpengine.netdna-ssl.com/wp-content/uploads/tech_docs/tds/22058.pdf


  • Re: 912S3 strange cylinder #2 behavior

    by » 5 weeks ago


    Thank you for the tips, I'll try to have this checked during the next inspection which will be ... the first 100hrs on this engine (it has 70 hrs as of today).

     

    Nick.


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