Service Letter SL-912-16-r1 Errors

by Bill Hertzel in General Tech Discussion 7 years ago

Rotax has released and given notice of a revision to Service Letter SL-912-016-r1 today.

Page 7 contains some confusing instructions.
It appears that all instructions referencing the operation of the Choke are reversed from normal conventions.

A Cold engine start instructs starting with the Choke fully OPEN and the slowly CLOSING the Choke as the engine warms up. ???

A Hot engine start instructs starting with the Choke CLOSED. ???

A flooded engine start instructs opening the throttle fully with the Choke CLOSED to clear the flood. ???

Has something been lost in translation? :unsure:

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Service Letter SL-912-16-r1 Errors

by Alan Arnold » 7 years ago

Alan Arnold

20 188 145

It's not really a choke. It's an "enricher", so when it is open, it lets more fuel into the idle circuit of the carb.

Alan

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Re: Service Letter SL-912-16-r1 Errors

by Roger Lee » 7 years ago

Roger Lee

125 5.12k 4.53k

Hi Bill,

I'm not sure I see your inference?
How do you do it?
As far as I know most open or engage if you will the choke(enricher) fully on a cold start. Most of us with idles set down around 1600-1700 crack the throttle just a tad too. When the engine starts it's right about 2200 +/-rpm.

Warm starts we leave it closed.

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

Thank you said by: Volker Sobetzko

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Re: Service Letter SL-912-16-r1 Errors

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

All the dissenting opinions here had me thinking that dementia had set in. :ohmy:

I hope this long winded explanation will help but I am still not expecting any agreement.

As stated, the Bing Carbs have an "Enricher", any not a conventional Plate Style Choke.
When OPEN, more Fuel gets to the Engine, Richer. (Choked!)
When CLOSED, less Fuel gets to the Engine, Leaner. (Normal)

The Service Letter references the operation of the Choke as being OPEN or CLOSED.
Interestingly enough, this is the only Rotax document that directly references a Choke and Open and Closed.

The 912ULS Operators Manual references the device as the "Starting Carb (Choke)" [sic] and that it is to be ACTIVATED and DE-ACTIVATED as instructed. And never referenced to as Opened or Closed.

The 912ULS Installation Manual references the device as the CHOKE which is to ACTIVATED.
In another sentence, they advise that the Bowden cables should be adjusted such that the "...Throttle and Choke can be fully opened and closed", leaving the function of opened and closed up to the experience of the reader.

My Pilots Operating Handbook and the Checklists references the device as a CHOKE that is to be ENGAGED and DISENGAGED.
Interestingly, the control in the aircraft that is labeled CHOKE is marked as ON and OFF.

All was fine until the Service letter came out.
There is no problem with ACTIVATE = ON = ENGAGE and DE-ACTIVATE = OFF = DISENGAGE.

The problem is when the instruction says OPEN and CLOSE.
If you are intimately familiar with the Bing and other Motorcycle Type Carbs, you may understand that "CLOSING the Choke" means you are Closing the Enricher (Starting Carb) and Leaning the mixture and not actually closing a CHOKE PLATE and Enriching the mixture.

In the non-Bing, Automotive and lawn equipment world, that most people are familiar with, the Carbs have a visible Choke Plate at the entrance of the carb that is Closed during a Cold start to enrichen the mixture.

The confusion would be after reading the Service letter that instructs Choke OPEN and then going to your aircraft with a panel that is labeled Choke Engage, Activate, or ON. What position do you select?

I immediately assumed that OPEN meant the Choke (Plate) was to be Opened (Leaned).
After years of looking at the choke Graphics on my multitude of small engines, it has been engrained that Open = Run and Closed = Choked

At best, the use of OPEN and CLOSED should be avoided to prevent confusion to the average pilot that may only have a superficial understand of the detailed operation of the 912 carburetor in his aircraft as compared to the more common Choke Plate type Carbs. Alternatively, don't call it a CHOKE; Which it isn't.

Choke_2016-12-31.jpg (You do not have access to download this file.)

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Service Letter SL-912-16-r1 Errors

by Alan Arnold » 7 years ago

Alan Arnold

20 188 145

Sounds like there might be a "new guy" at Rotax that doesn't know the difference but was tasked with writing this service letter.

Alan

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Re: Service Letter SL-912-16-r1 Errors

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

Rotax does not give access to the Service Letter Archives as far as I can find.
It would be interesting to see if the OPEN/CLOSED references were used in the revision Zero Service Letter.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Service Letter SL-912-16-r1 Errors

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