Rotax 912 ULS cold start

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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3Dreaming
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Re: Rotax 912 ULS cold start

Postby 3Dreaming » Mon May 13, 2019 8:52 am

rcpilot wrote:
Warmi wrote:I am at 350 hours , the 5 years rubber was done in late 2017 and the carbs were looked at as part of annual a month ago - how do you tell if it is time to have them rebuild ?

The carbs are supposed to be "rebuilt" every 5 years also. Replace the gaskets, O rings, etc. and check the weight of the floats and replace them if needed.


The carbs are supposed to be disassembled for inspection every 200 hours. The float weight is supposed to be checked every 200 hours or annually.
Also a reminder that in FAA speak a mechanic is not allowed to rebuild the carbs. They can inspect, overhaul, and repair. Rebuilding is only allowed by the manufacturer or an agent under their direction.

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ShawnM
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Re: Rotax 912 ULS cold start

Postby ShawnM » Mon May 13, 2019 8:55 am

Warmi wrote:I have the soft start ignition modules and they do work , there is marked RPM jump after about 2 seconds - which is where it gets smooth, it is the first 2 seconds where the engine is jumpy and rough.

When it is 65+ F or so , the engine pretty much starts right away - the issue only occurs when it gets below 60-55 F.

Shawn:
Would it be possible for you to record the startup procedure on your plane when it is colder outside ( which by Florida standards probably means 60+ degrees :-) ) ?


After 2 seconds? Are you certain you have the soft start modules? Are they Rotax? Rotax says 5-8 seconds for them to turn off. Do you have an aftermarket soft start module? My soft start delay is about 5 seconds and it is still pretty smooth when it's enabled and gets noticeably smoother after it turns off and this happens when I'm rolling off the choke and adding a little throttle. I'm careful to add just a little throttle because when the soft start kicks off the rpm jumps a couple of hundred when it does. I'm just careful to stay under the 2500 threshold.

Um, yeah, it's now May here in Florida and I probably won't see temps in the 60's again until MAYBE November. :shock:

Sit tight , I'll get you that video then. :mrgreen:

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Warmi
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Re: Rotax 912 ULS cold start

Postby Warmi » Mon May 13, 2019 9:15 am

Well, maybe it is 5 seconds - you can see on my second video in the thread when it gets smoother :-)

This weekend I went for a flight in a 2007 Remos in a local flight school (just for fun ) and the plane started in similar fashion as my Sting .
Flying Sting S4 ( N184WA ) out of Illinois

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Re: Rotax 912 ULS cold start

Postby roger lee » Mon May 13, 2019 9:18 am

There is nothing in any Rotax publication that says when carbs are to be overhauled. Only inspected is in writing every 200 hrs.
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dstclair
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Re: Rotax 912 ULS cold start

Postby dstclair » Mon May 13, 2019 10:23 am

Smarter people than me can opine but I'm pretty sure your roughness on a cold start is due to your idle. A cold start requires the 'prime' on and the throttle closed. This means you're pretty much at the 1600 rpm level on start which in the Sting I flew for 11 years would've been rough until I bumped the throttle open a bit. YMMV.
dave

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ShawnM
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Re: Rotax 912 ULS cold start

Postby ShawnM » Mon May 13, 2019 10:26 am

Warmi wrote:Well, maybe it is 5 seconds - you can see on my second video in the thread when it gets smoother :-)

This weekend I went for a flight in a 2007 Remos in a local flight school (just for fun ) and the plane started in similar fashion as my Sting .


Sorry, can't really see it in the second video either and I doubt one could, it's more "feeling" it when they turn off. Is yours an aftermarket soft start or the OEM Rotax ignition modules? You didn't say.

Unless the 2007 Remos has had it's ignition modules replaced it wouldn't have the soft start feature either. Rotax didn't introduce this until late 2010 I think. Do your ignition modules have a green or yellow sticker? Even when you install the new "yellow sticker" ignition modules you have to add 2 wires to your harness ( or a "Y" wire) to actually activate the soft start feature of those ignition modules. Just food for thought.

I'm still slowly closing the choke and advancing the throttle slightly when you are turning on all your switches. :mrgreen:

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ShawnM
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Re: Rotax 912 ULS cold start

Postby ShawnM » Mon May 13, 2019 10:28 am

roger lee wrote:There is nothing in any Rotax publication that says when carbs are to be overhauled. Only inspected is in writing every 200 hrs.


Good to know, thanks Roger.

If it ain't broke........... :mrgreen:

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ShawnM
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Re: Rotax 912 ULS cold start

Postby ShawnM » Mon May 13, 2019 10:30 am

dstclair wrote:Smarter people than me can opine but I'm pretty sure your roughness on a cold start is due to your idle. A cold start requires the 'prime' on and the throttle closed. This means you're pretty much at the 1600 rpm level on start which in the Sting I flew for 11 years would've been rough until I bumped the throttle open a bit. YMMV.


I sort of have to agree with this. It seems to smooth out when he adds in some power to get it above idle right after it starts.

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Warmi
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Re: Rotax 912 ULS cold start

Postby Warmi » Mon May 13, 2019 10:35 am

ShawnM wrote:
Warmi wrote:Well, maybe it is 5 seconds - you can see on my second video in the thread when it gets smoother :-)

This weekend I went for a flight in a 2007 Remos in a local flight school (just for fun ) and the plane started in similar fashion as my Sting .


Sorry, can't really see it in the second video either and I doubt one could, it's more "feeling" it when they turn off. Is yours an aftermarket soft start or the OEM Rotax ignition modules? You didn't say.

Unless the 2007 Remos has had it's ignition modules replaced it wouldn't have the soft start feature either. Rotax didn't introduce this until late 2010 I think. Do your ignition modules have a green or yellow sticker? Even when you install the new "yellow sticker" ignition modules you have to add 2 wires to your harness ( or a "Y" wire) to actually activate the soft start feature of those ignition modules. Just food for thought.

I'm still slowly closing the choke and advancing the throttle slightly when you are turning on all your switches. :mrgreen:



I got the yellow sticker , it is a mid 2012 model so it already has soft modules installed.
I am pretty sure , what dstclair is suggesting about the low idle is probably the culprit.

PS.
Sorry about all these questions but these sort of conversions, as recorded on this forum, may be of help to someone else looking for answers ...
Flying Sting S4 ( N184WA ) out of Illinois

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Re: Rotax 912 ULS cold start

Postby Wm.Ince » Mon May 13, 2019 10:46 am

ShawnM wrote:I have the soft start ignition modules so I can't really compare my starts to yours. Like Bill, my plane starts instantly every time. I also agree that your idle is too low. Mine is set for 1750-1800 and settles in this range somewhere. I never idle it below 2000 once started for the sake of the gearbox. Well, let me rephrase that, during my runup I check that the plane will go to idle without dying after I do my mag check. Then it's back to 2000+ RPM.

My start procedure is exactly as Bill explained. As soon as the engine comes alive I slowly roll off the "choke" while adding in a little power at the same time to keep the idle between 2000 and 2200 after it starts. During this dance on the choke and throttle levers my soft start modules kick off after about 5 seconds and the rpm increases a little after that.

I also agree that if you have the choke (fuel enrichment circuit) on during a cold start the throttle needs to be completely closed or it defeats the purpose of the "choke". None of this "crack the throttle 1/4" nonsense regardless of what your POH says. Ask any Rotax certified mechanic. :mrgreen:

Concur totally.
Bill Ince
CTSW (E-LSA)
Retired Heavy Equipment Operator

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drseti
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Re: Rotax 912 ULS cold start

Postby drseti » Mon May 13, 2019 12:15 pm

Warmi wrote:how do you tell if it is time to have them rebuild ?


Rotax says every 200 hours.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
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drseti
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Re: Rotax 912 ULS cold start

Postby drseti » Mon May 13, 2019 12:18 pm

FastEddieB wrote:The “choke” - not really a choke -


True. It's really an enricher.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
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