I bought the plane with 150 hours, and from what I can tell it has been sitting most of its life. When I got it it went through annual, and everything seemed to check out ok. Not having any prior rotax experience I had no idea what was normal until I went and got my type specific training and immediately knew I had a problem with mine. Before I rebuilt the gearbox it used to make a horrible ratcheting sound below 2500- so thats when I started on my long saga. After rebuilding he carbs a second time I had a rotax tech look at it and he said the gearbox needed to be reshimmed which helped but did not fix the problem. The original owner says the plane has always been that way- so as far as I know its had this problem since birth. I have included pics of the dog gear so you can see the wear- thats why I replaced the gearset and dog gear. Since I have done that it is quite a bit better but still not right.
image_2014-04-02.jpg (You do not have access to download this file.)
image_2014-04-02-2.jpg (You do not have access to download this file.)
Did you look at the ignition leads, where they connect to the spark plug caps? They just thread into the caps, and if the cap isnt on properly or far enough to make a good connection, it can cause rough running issues more noticable at low rpm.
Do you have an overload clutch? If so, what was the friction torque after you rebuilt the gearbox?
Yes- I just checked all the wires with a inductive timing light, then I taped off the leads to check depth on the NGK spark plug caps, checked resistance on the spark plug caps(5kohm). This does not have a clutch in the gearbox.
Well, I'm out of ideas on this one at the current moment without doing more research, but you might want to try giving Lockwood a call... One of the few 912 Rotax overhaul shops in the US. They have a tech support line open from 9am-10am and 2pm-3pm daily. 863-655-6229 Extension 3. They might be more help on this issue. I'd hate to see you throw more money at the problem without diagnosing the root cause first.
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