912UL runs rough on start to 2500rpm

by Glynn McGregor in 912 / 914 Technical Questions 10 years ago

Hi I'm working on a Xenon gyro copter which has the 912UL Rotax engine with a Subaru turbo on it as a modification for much better performance.The engine runs VERY rough on start up and continues to run rough on idle, as you power up the serious rough running gets less, at approximately around 3000 RPM the engine begins to run smoothly, removed and serviced both carbs checked all plugs, and check the CDI boxes, also done a full electrical check, what else can i do?

Re: 912UL runs rough on start to 2500rpm

by Roger Lee » 10 years ago

Roger Lee

125 5.12k 4.53k

Hi Glenn,

You may be a little on you own here and experiment some because 99.9% of the ULS owners don't have a setup like this. I personally don't know either.

Sorry, would help if I could.

How about someone that sold you the turbo and said it would work?

Give Ronnie Smith a call from South Mississippi Light Aircraft. He might be able to help.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 912UL runs rough on start to 2500rpm

by Glynn McGregor » 10 years ago

Glynn McGregor

1 1 0

Hi Roger,

The Xenon gyro company does the turbo as a standard modification to the engine, they say once the engine has been modified to there specifications they call it the RST motor.

I seemed to have sorted the problem out,it was a matter of really fine tuning those carbs to synchronize with the engine due to the turbo kicking in right at start up unlike the Rotax914, so it was a matter of fine tuning the air/fuel mixture and idle and carb balancing all in one.

Thanks for your reply.
most appreciated

Thank you said by: YEN NIEN YU

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Re: 912UL runs rough on start to 2500rpm

by Roger Lee » 10 years ago

Roger Lee

125 5.12k 4.53k

Hi Glenn,

Glad you got it fixed. I have no experience with that setup, but now I'll tuck that little tidbit in my mental toolbox.

Have fun with your Gyro

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: YEN NIEN YU

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912UL runs rough on start to 2500rpm

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