We use a 914 in our tug aircraft, a Super Dimona. Last month it suddenly started running rough at low power settings. We have replaced the floats and the diaphragms on both carbs, inspected the pneumatic lines and found no pin holes, tested the compressions on each cylinder, all showing OK. The plugs indicate that 3 of the four cylinders are running rich and one set of plugs is "normal". The plugs themselves are almost new. We have checked the grounding on the ignition modules.

This afternoon a light tap on one of the carbs resulted in the engine running beautifully smoothly for a short while, but then the rough running returned. 

The engine is being run on mogas with the usual European 5% ethanol content.

Any/all suggestions welcome





  • Re: 914 rough running at low revs

    by » one month ago

    Check the bowls and low speed jets for dirt and corrosion. Actually take the low speed jet out and inspect, it has small holes in the side of it. And make the carbs are balanced.

    Thank you said by: Peter Harvey

  • Re: 914 rough running at low revs

    by » 6 weeks ago

    make sure the carb throttle stop and lever brackets are not bent, the HK36 has a lot of leverage on the cables.

    if it is bent, straighten them out and then adjust the throttle cables so the cockpit control hits the end of the slot slightly after the carb leaver hits the idle stop screw. This prevents the pilot from bending the bracket.

    and then make the fine adjustments with a pneumatic carb sync. Be fussy that the sync is good, even when you pull hard on the throttle control. After a little “bounce” it should hit the cockpit stop and not be bending the stop screw bracket.

    Thank you said by: Peter Harvey

  • Re: 914 rough running at low revs

    by » 2 weeks ago

    Problem solved, it turns out to have been a broken circlip at the bottom of the main jet, replaced both the circlip and the related o-ring, engine now runs as smooth as anything

    Thank you said by: RotaxOwner Admin, Bill Hertzel

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