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Hello, I have a new to me Onex with a Turbo Aerovee engine on it. It has about 7 hours running time and 3 flights. After a long trailer trip, I started going through everything. I warmed the engine, taxied it around a bit.. (a little touchier on the ground than my legacy Sonex but not bad). Startup seemed smooth enough so when I did an ignition check and dropped the 12V ignition, I got a fairly sever drop in RPM, So I quickly turned 12V back on. Then killed the mag side and also got quite a drop but not quite as severe. Not to worried about the 12V yet but I am concerned that the mags run so poorly alone. This video will give you an idea. Hope to get a better one. Thoughts on where to start troubleshooting the Mag side?

https://youtube.com/shorts/Ju4kqIWh_cM

My engine is a non-turvo AeroVee. The manual for it says if there is more than a 50 rpm drop, that there is a problem with the timing. The primary ignition timing is fixed but the secondary, 12 volt, can be adjusted. The manual explains how to do that.

There is also a post on this site that explains it better and suggests doing a test flight, running for 5 minutes on primary, then secondary, and then there is a software program you can buy to analyze the CHT's. It will let you find the average of the CHT's when running on each ignition system. Then if they are near one another, it is adjusted correctly. If there is a large gap, the manual tells you which direction to turn the secondary ignition.

I don't know if that procedure applies to the turbo version. I hope this helps.

pilotyoung wrote:My engine is a non-turvo AeroVee. The manual for it says if there is more than a 50 rpm drop, that there is a problem with the timing. The primary ignition timing is fixed but the secondary, 12 volt, can be adjusted. The manual explains how to do that.

There is also a post on this site that explains it better and suggests doing a test flight, running for 5 minutes on primary, then secondary, and then there is a software program you can buy to analyze the CHT's. It will let you find the average of the CHT's when running on each ignition system. Then if they are near one another, it is adjusted correctly. If there is a large gap, the manual tells you which direction to turn the secondary ignition.

I don't know if that procedure applies to the turbo version. I hope this helps.

Link to the video referred to above: https://www.youtube.com/watch?v=bMWfEA8s8so

Thanks, This is all very helpful.

Listening to your video, at least one cylinder isn’t firing on either ignition, explaining the rpm drop. The engine starting easily and running nicely with both ignitions, suggests it’s a spark problem. The engine has a lot of ground time compared to flight time, and presuming you purchased it, several prospective buyers may have asked to hear it run also, it may just be a couple fouled spark plugs. Try putting fresh plugs in it before diving too deep.

Waiex 0194 wrote:Listening to your video, at least one cylinder isn’t firing on either ignition, explaining the rpm drop.

After reading your comment, I re-watched the video and noticed the EGT on Cylinder 2 drops rapidly at the beginning of the video. Not sure, but I think it's when the 12V ignition is switched off.

Larry, Chris Good catch. Based on your observations, I went back out and ran it again, and with some help, found a bad lower magnatron. Will replace it and post later. Again Thanks. (PS previous Aerovee owner/builder came by the hangar and helped me chase it. I showed him your posts and he went. Ah hah!!