EGT 200 f increase and 500 RPM drop on mag check

Paul Hamilton wrote:

Makes most sense that intermittent running at midrange flying would be Carbs. 

Makes sense that mag drop on upper verses lower would be different based on fuel/air entering top but typically ROTAX specs should be reasonable to hit with this situation.

Makes sense that one mag running good and one bad would be electric since the carb is operation great with one mag side.

Just talked with a pilot who was having the same problem. I advised him to switch the electronic module boxes out and try it. (Now I am wondering how this was done because when I look at it closely it does not look like they can be easily switched? A top and B bottom clearly labeled and flipping over would cross the in/out wires) He did mag check and same mag was bad. He switched both boxes out with new ones and it fixed problem. This makes no sense.

Has anyone had any problems with the ignition coils? I have had two go bad with my 912iS.

Thanks for all the help.....

The modules are easy to switch. “A” and “B” are meaningless labels for each of the circuits. I had to use sharpie to label my connectors to make sure the “B” box was going to the formerly “A” connectors on each side, and likewise for the “A” box. The in/out wires should be switched to the other respective circuit, which makes the new A top and B bottom (with labels reversed) easy to fit back into place. The modules swap positions and in/out connections, switching each module onto the other wiring circuit. 

Nicholas Wilcox wrote:

Paul Hamilton wrote:

Makes most sense that intermittent running at midrange flying would be Carbs. 

Makes sense that mag drop on upper verses lower would be different based on fuel/air entering top but typically ROTAX specs should be reasonable to hit with this situation.

Makes sense that one mag running good and one bad would be electric since the carb is operation great with one mag side.

Just talked with a pilot who was having the same problem. I advised him to switch the electronic module boxes out and try it. (Now I am wondering how this was done because when I look at it closely it does not look like they can be easily switched? A top and B bottom clearly labeled and flipping over would cross the in/out wires) He did mag check and same mag was bad. He switched both boxes out with new ones and it fixed problem. This makes no sense.

Has anyone had any problems with the ignition coils? I have had two go bad with my 912iS.

Thanks for all the help.....

The modules are easy to switch. “A” and “B” are meaningless labels for each of the circuits. I had to use sharpie to label my connectors to make sure the “B” box was going to the formerly “A” connectors on each side, and likewise for the “A” box. The in/out wires should be switched to the other respective circuit, which makes the new A top and B bottom (with labels reversed) easy to fit back into place. The modules swap positions and in/out connections, switching each module onto the other wiring circuit. 

Ok just checking…….

Mike Montefusco wrote:

How many hours since your carbs were rebuilt?

This ended up being the cause. Maintenance logs from previous owner didn’t show a carb rebuild over its 12 years of life. Dean at Lockwood had us do a choke test (run to the 4000pm where it has issues, put choke on during mag test, and see if it gets smoother or rougher), and it did get change things, indicating carb issue. We also swapped horizontal and vertical connector plugs into the control boxes and rough running swapped sides, indicating issue was further downstream - likely carbs. Lockwood did the 5 year rebuild, we reinstalled, and issue is now gone. Seems like input on EGT rise was also correct: extra fuel from midrange leak was igniting at the glowing EGT sensor on that side, causing EGT to rise with extra RPM drop. Thanks to all for input.