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Rotax 912ULS Starting and Maintenance Problems

PostPosted: Fri May 04, 2007 10:08 am
by copilot 1
I have a new SLSA equipped with the 912ULS. This  engine is one of the most unreliable I have ever owned. Temperatures below 45 degrees require preheat and then it is questionable. The Starter is not capable of cranking the engine without lockup as a result of the ignition system not providing for spark retard during the start cycle. The spark is always advanced. The result is the engine attempts to run backwards.

Due to "Rotax not being able to design a single point throttle cable system they leave the responsibility up to the aircraft designer to figure something out. The net result of this lack of engineering is evident in the reams of paper on how to balance the Bing carbrueators. Maintaining sync on any kind of a long term basis ( at least 5 or 10 hours ) doesen,t seem possible. To have this done by a mechanic  is a 60 dollar job !!  When the thing goes out of sync the vibration and noise level at any engine speed becomes obnoxious.

Parts costs are another issue. Failure of the antiquated ignition module is a $1200 bill and another $60/100  for installation !!

I wonder what the expirence of others is with this engine ?? And are there solutions ??

PostPosted: Wed May 30, 2007 8:40 am
by alan

I'm sorry to hear about your 912ULS problems. I have had none. My starter always spins the motor over briskly, every time. I live on the Texas gulf coast, so it is not often below 45 degrees, but we have flown when the temps are down in the 30's with no problem. I was under the impression that the ignition system varied the timing to suit the circumstanses. Are you sure about it "always being advanced"? If it is, it should be a warranty claim to fix it.

As to the throttle cables, I bought mine from Just Aircraft. It is a quality piece and keeps the carbs synched. I don't know if it would be legal to swap out any parts on a SLSA, so this info might not help.

We have 140 hours on our 912ULS and couldn't me happier, so far, knock on wood.


PostPosted: Wed May 30, 2007 9:20 pm
by copilot 1
Alan----Thanks for the reply with your expierence with the 912.
Several points --Yes I have researched the ignition system. The timiing is fixed and no changes occur during operation. The firing point is always advanced. The modules are Ducati motorcycle ignitions  modules.

I think I have a solution to the problem. One is a larger battery and the second is heavier cabling between battery and starter. I have also been tolt ptoblems will occur if the battery ages or the output for cranking falls off.

The throttle system is another issue which goes back to Rotax not providing a standart single point connection for the throttle. Also the system on my plane (Aerostar R40S) is a poor design for the throttle linkages from Aerostar.

I will look into your linkages and see how they could be adapted. As a further point of interest I have been told Rotax is going to make available a single point throttle system. This as a result of Cessna's expierence with the 91

Thanks again Milt K

PostPosted: Thu Feb 12, 2009 1:32 pm
by fly away
Hi copilot 1,

synchronizing the carburetors is indeed very important in order to reduce vibrations and to improve start-up procedure.

Most of the synchronizers have a scale rang 0...29,5" HG - too large!;

I have made best experiences with the synchronizer from a german company. The scale range 0...17,7HG for the rotax 912 and scale range 0...11,8"HG for the rotax two stroke enables you to synchronize your carbs in a perfect manner. The company is specialized in producing synchronizers for carbs. The gauges are equipped with capsule pressure gauges with zero adjustment.

PostPosted: Fri Feb 20, 2009 9:05 pm
by Doug W.

I have 350 hrs. on my 912 ULS. It is on a Magni M-16 gyroplane. All installation items were supplied with the kit. We balanced the carbs at installation and have touched them since. It has always started with ease from 100 degrees down to 20 degrees. I am still running on the original 2 year old battery. I have always described my engine as bullet proof.

I hope you can resolve your problems!