912 ULS starting but stalls

Sean Griffin wrote:

Hi Jeffrey,

Please list your, cold engine, starting methodology?😈

Throttle off.

Choke on.

Turn key.  

As soon as it fires - less than a second - release key.

Idles rough for 3-4 seconds then jumps to faster idle.

Advance throttle while removing choke and warm at ~2000rpm

For years.  Now it is different.

Rotax-Owner wrote:

There appear to be several different starting procedure methods mentioned in this forum, so we will provide the one specified in the Rotax Operator's Manual (referenced in the attachment)

Now that you have the official starting procedure, there are a few additional things to consider.

You mentioned that your idle RPM is 1,745 RPM after warm-up, which is too low and can lead to premature gearbox and carburetor wear, potentially causing starting issues. (Minimum recommended idle speed is 2,000 RPM)

Since you have been idling below 2,000 RPM, it might be a good idea to check the friction torque on your gearbox. This is a simple procedure that should be done every 100 hours to ensure the gearbox remains within limits. An out-of-spec gearbox could cause the engine to run rough, especially at idle, which may exacerbate starting issues.

(Friction Torque inspection procedure Video): https://www.rotax-owner.com/en/videos-topmenu/elearning-videos/60-friction-torque29

If you provide your engine S/N, we can check whether your engine is equipped with the Advanced Start Module. It is also important to have a strong/properly charged battery. A low battery may not allow the starter to spin the engine fast enough, which can cause starting issues.

That is the procedure for years.

The engine does not reach the first part of #7.

The original factory set-up was 1850rpm.  Even at that rpm the trike will wear brakes rapidly.  Part of flying business?

Friction torque is within normal limits.

It has alway run rough for the first 3-4 seconds.  Till it "catches" then immediately runs better and smooths out completley when the choke is turned off.  Usually in less than 15-20 seconds.

I will start with raising the idle I guess.

Thank you.

edit: SN-957-3470

Okay - some small, possibly irrelevant differences;

No mention of Boost Pump ON before cranking - primes system, confirms operation - Off again before cranking.

Mine has no rough idle when Choke ON,  full or 1/2 .

When Choke OFF  - very very minor roughness, disappears as engine warms.

Auto fast idle starts within a second or two of start (thats when I remove all Choke).

Q. Has anyone worked on the carburettors in recent times? (5 year rubber replacement?)😈

Jeffery,

You should raise the idle to a minimum of 2,000 to avoid gearbox wear, but not to solve this problem. If it started fine before it should start now. It sounds as if your soft start module is malfunctioning. But, modern electronics are quite reliable, so maybe try simpler things- like mechanical linkages that move and wear. Is your cold start (“choke”) linkage checked? Both choke carb lever arms contact the carb stops at fully open and fully closed? Does your choke control knob stay put after the engine fires or does it immediately begin to move towards the closed position when the engine starts due to vibration as Sean’s does? Mine does this as well- if I don’t hold it open with a finger it will close rapidly when the engine fires and the engine will run rough or die. Once my soft start module returns the ignition timing to normal she smooths out a bit but will still run slightly rough until I close the choke, then she smooths out nicely. All this happens within a few seconds on my 912UL.

Sean Griffin wrote:

Okay - some small, possibly irrelevant differences;

No mention of Boost Pump ON before cranking - primes system, confirms operation - Off again before cranking.

Mine has no rough idle when Choke ON,  full or 1/2 .

When Choke OFF  - very very minor roughness, disappears as engine warms.

Auto fast idle starts within a second or two of start (thats when I remove all Choke).

Q. Has anyone worked on the carburettors in recent times? (5 year rubber replacement?)😈

Electric pump on for starting and sometimes left on for flight.  

Fast idle has always taken 3-4 seconds. How do I make it happen faster?

Four years old. Hobbs is 330.

Two 200 hour services on the carbs by Lockwood in the first two years. Plus one return after first service because the throttle would not close on one of the carbs. "There was a burr on it" No paperwork.