914 UL Vibration

by Tim Cray in 912 / 914 Technical Questions 8 years ago

I am working on a 914 UL that will not throttle past 3200 rpm and vibrates like mad and when I try to throttle up quickly it vibrates and chokes. I have had the carbs and gearbox checked out and were O/K, Iv'e replaced the vent lines on the air box and carbs. The rubber flanges on the carbs appear to be fine, the plug gaps are set at 0.25 and the carbs are balanced. Iv'e had to replace the three stainless steel bracket that are on the turbo and exhaust that were shattered and am currently replacing the TCU (turbo control unit) which is not operating the waste gate. Does anyone have any ideas or experienced the same problems that can help.
Thanks in anticipation.

Re: 914 UL Vibration

by Walter Sauerborn » 8 years ago

Walter Sauerborn

0 3 0

Hi Tim,

great caution by operating the 914 without Wastegate Control by the TCU.
Normaly, TCU off or out of function, or circuit breaker for tcu off, the wastegate is fully open. Check the manifold pressure at your Instrument at idle Speed and low rpm up to 3000 rpm.
My experience was an catastrophical overboost at takeoff, caused by an damaged circuitbreaker for the tcu. There was no power for the tcu, and wastegaste was open, nobody looked at the manifold pressure Instrument during takeoff-run.
We had catastrophical vibrations during the overboost, the crancshaft was destroyed.
Check both tcu Control lights after Power on, they must lit during the self test of tcu, and the servo for the wastegate is pulled to closed and back in Position full open. You can hear this noise by the Servomotor after power on by Battery masterswitch.
If the wastegate is in the fully open Position, at idle Speed, your manifold-pressure indication is the atmospheric pressure 29-32inch. If you Speed up light, the maniflod pressure increases very fast, if you move the throttle forward very carefully.
Normally the tcu makes his Job and closes and opens the wastegate in dependence of the manifold pressure. The tcu regulates the manifold pressure at a constant Level at 30 - 32 Inch up to 100 % Throttle.
Over 100 - 115 % the manifold pressure increases up to 40-42 Inch to reach the power of 115 hp.
Never use the engine without optimal working tcu, overboost kills the engine in 20-30 seconds of full power.

I hope, i could help you, please give me an Feedback of your inspection.

Best Regards from Walter in Germany

Thank you said by: Tim Cray, RotaxOwner Admin

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Re: 914 UL Vibration

by Tim Cray » 8 years ago

Tim Cray

3 4 16

Thanks Walter, I'm waiting for the new TCU before I run the engine again, I'll let you know when I receive it. Cheers Tim

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