912UL Engine vibration on throttle back
in 912 / 914 Technical Questions
12 years ago
Gents I need some advice.
I have a 2003 Evektor Eurostar with a 912UL running a Woodcomp Klassic 3 blade fixed pitch prop. The engine has done about 700 hrs. Max static RPM is about 4800 and idle about 1400.
The engine has been well maintained and has worked flawlessly since I bought the plane 4 years ago. Just recently I have noticed a problem. If I am in the cruise at about 4400rpm the engine is smooth. When I throttle back it becomes rough and the roughness is noticeable on the rev counter with the needle oscillating instead of remaining steady. It is not a severe vibration but it is noticeable.
Sometimes the problem would go as quickly as it came. Other times it could be cured by applying power back to cruise setting.
More recently I have noticed that the vibration is not so quick to go and reapplying cruise power no longer fixes the problem.
I have looked through the various 'vibration' related threads and I see that there are a number of issues to look at. This is what I have looked at so far:
It does not seem to exhibit the problem when in the climb. It is more likely to be when off load, either slowing in the cruise or during descent.
I have not checked the prop balance or blade pitch. As far as I am aware nothing has been changed on the prop and the gearbox was serviced and reshimmed at 400hrs.
I might see if I can pick up the vibration using my iPhone microphone and trying to see the frequency of the vibration using one of the free spectrum analyser apps. That might tell me whether it is a prop blade problem or an engine problem.
Any other thoughts and suggestions would be gratefully received.
Regards,
Kevin
I have a 2003 Evektor Eurostar with a 912UL running a Woodcomp Klassic 3 blade fixed pitch prop. The engine has done about 700 hrs. Max static RPM is about 4800 and idle about 1400.
The engine has been well maintained and has worked flawlessly since I bought the plane 4 years ago. Just recently I have noticed a problem. If I am in the cruise at about 4400rpm the engine is smooth. When I throttle back it becomes rough and the roughness is noticeable on the rev counter with the needle oscillating instead of remaining steady. It is not a severe vibration but it is noticeable.
Sometimes the problem would go as quickly as it came. Other times it could be cured by applying power back to cruise setting.
More recently I have noticed that the vibration is not so quick to go and reapplying cruise power no longer fixes the problem.
I have looked through the various 'vibration' related threads and I see that there are a number of issues to look at. This is what I have looked at so far:
- Carb sync (which is good)
- Carb diaphrams for splits
- Carb pistons for sticking
- Throttle cables seem smooth
- Main needles
- Main jets
- Engine mounts
It does not seem to exhibit the problem when in the climb. It is more likely to be when off load, either slowing in the cruise or during descent.
I have not checked the prop balance or blade pitch. As far as I am aware nothing has been changed on the prop and the gearbox was serviced and reshimmed at 400hrs.
I might see if I can pick up the vibration using my iPhone microphone and trying to see the frequency of the vibration using one of the free spectrum analyser apps. That might tell me whether it is a prop blade problem or an engine problem.
Any other thoughts and suggestions would be gratefully received.
Regards,
Kevin
