912UL hesitation / stutter

by John J Reichart in 912 / 914 Technical Questions one year ago

Can anyone identify this... anomaly? Not sure what else to call it. Starts at 10 seconds in the video. There is a additional buzzing before/after in the video, but I've go that figured out - that was a loose baffle in the muffler. It's much quieter now.

The engine looses about 100 RPM for a fraction of a second when it makes this noise.

It does not happen on the ground, making it difficult to troubleshoot. Does not happen below 5000 RPM. Seems to happen while climbing at or above 5000 RPM.

Could it be detonation? Pre-ignition? Intermittent vacuum leak?

https://www.youtube.com/watch?v=sApglxgRX_Y

Thanks!

Re: 912UL hesitation / stutter

by Rotax-Owner » one year ago

Rotax-Owner

9 683 2.14k

It appears you may be experiencing an ignition switch problem. The RPM loss could be due to one of the magnetos shutting off, possibly caused by a loose connection in your switch. Are you using toggle switches, or is it a rotary switch?

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Re: 912UL hesitation / stutter

by John J Reichart » one year ago

John J Reichart

2 2 8

It is a rotary switch.

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Re: 912UL hesitation / stutter

by David HEAL » one year ago

David HEAL

23 191 439

Perhaps it is not from the engine -- airframe buzz, loose panel or wire somewhere?? As R-O noted above, the drop in RPM appears to be similar to one mag momentarily turning OFF. If one mag is turning OFF you should see a corresponding increase in the EGT for the cylinder bank associated with the OFF mag.

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912UL hesitation / stutter

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