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Permalink Reply by Stephen R. Smith on Monday

Well I would not fly it again until you find the issue. It could be a loose throttle cable. If it came completely loose in flight, that would not be fun at all. If the cable is not loose there are a few other things to check.

When the throttle is closed, what limits its travel? There is an idle speed adjustment screw on the passenger's side of the carb. The bracket that the screw is fixed to is quite flimsy and was not intended for the stout throttle cables we use on aircraft. In any case, you need to investigate whether the idle speed adjustment screw is being used or if there is some other mechanical stop (which is what I did on my airplane).

Another possible cause of a higher idle could be a vacuum leak. There are a number of trouble points that can cause a vacuum leak on a Jabiru: 1) the 6 rubber joiners that splice the two-part intake runners together, 2) the 6 O-rings that seal the intake runners to the intake manifold, 3) the rubber boot that connects the carburetor to the intake manifold which sometimes crack with age and vibration, 4) there is a vacuum port on the bottom of the carb. On my airplane I have a line running to a vacuum sensor. If that line came loose or got a crack, I would expect it to change the idle speed. If you don't have a hose connected to the port, is the plugging screw still present?

Let us know what you find.

Steve

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Permalink Reply by Rich Astley on Monday

Thanks for your replay Stephen,
I'm going to swing by the hangar this afternoon to see what I can see visually.  I'm hoping to have some time on Thursday morning to do some further investigation.

I'll report back in due course.

Cheers
Rich

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Permalink Reply by John Burns on Monday

If it has the standard Bing Carb and the Arion Aircraft Throttle lever extension there is enough leverage to bend the idle stop on the carb.  The solution is to get a cable stop to put on the cable so it hits the cable sheath and limits the cable travel at the idle RPM.  

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Permalink Reply by Rich Astley on Monday

Thanks John,

Yes, it is the standard carb - not sure about the throttle extension though.  I'm going to head to the hangar this afternoon to take a look and then Thursday morning for some further investigation.

Cheers
Rich

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Permalink Reply by Rich Astley on Tuesday

Looks like it was where the throttle sleeve was connect on the firewall before going to the throttle doubler bar (dual throttles).

I'm going to try and go on a test flight tomorrow morning

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