Jabiru Service Advisory
Subject: Rough running at idle power
Applicable: Jabiru Engines 22A
Compliance: Advice Only
Date: 12th Nov 2000

Rough running at idle power

There has been a small number of cases where the engine has developed rough running at idle power either whilst on the ground or when power is reduced to a low setting during descent.

The first action is to apply carb heat and increase the power setting to see if roughness disappears. If in flight make a powered approach keeping the power setting outside the rough range and land as normal. Remember that carb icing is likely on the ground in winter so if after 30 seconds of heat applied the roughness disappears then it was icing. During winter always close the throttle completely prior to lining up to check for irritate idle or stoppage, if these symptoms are present apply heat for 30 seconds and re-check.

If rough running is still present allow engine to cool down and remove cowlings to allow access to all four exhaust manifolds. Then re-start the engine and set the power so that the rough running is present and run the engine for 2-3 minutes then stop the engine.
With care not to bum your fingers check each exhaust manifold close to the cylinder head to see if one is cool or cold compared with the other three. If one manifold is found to be cool this is the problem head, so note its position. There is a very easy in-situ fix that _ takes less than 30 minutes to perform and requires no special skills. Contact ST Aviation and they will supply a simple fix kit and tool.

This problem has only manifested itself upon 0.4% of UK cylinder heads, and in flight can be remedied by increasing power, so it is not considered a high risk, but knowledge is safety so you can spot the problem if it arises.
Circulation:
All STA Jabiru builders and owners, Jabiru owners club, PFA Engineering, BMAA Engineering, Jabiru West & Jabiru Aircraft Pty Ltd.