ROTAX 912 series float trouble

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SOUT (RIP)
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ROTAX 912 series float trouble

Postby SOUT (RIP) » Wed Feb 18, 2015 11:20 am

Good day Flyers
I trust you are well

As a manufacturer / AP we are constantly asked "how do I check my 912 floats for their condition"
I am sure the experts on AVCOM (geniuses) have many scientific explanations on how to do and don't check them but here is my explanation.

If you are one of the unfortunate users of the flawed floats you will have an overflow of fuel at some stage. this is due to the float getting saturated with fuel while trying to float on the surface of the fuel (the one and only function of the float) while it floats it then pushes on an arm that closes the "valve" (needle and seat) in the float bowl at a pre set level. this cuts the fuel off from the fuel supply and maintains the pre set fuel level. the engine uses the fuel and the level drops inside the float bowl thus the float goes down with the fuel level. when the floats go down the arm goes down and re opens the "valve" (needle and seat) to the fuel supply filling the float bowl again. this happens constantly and very often in the course of flight. I expect the AVCOM geniuses to elaborate on this explanation and either correct or quote me incorrectly :lol:

The trouble
if you have saturated floats, the float does not float correctly on the fuel as was designed, it sinks. this sinking into the fuel changes the angle of the little arm in the float bowl that in return does not close the "valve" (needle and seat) to stop the fuel from the fuel supply at the pre set level and your carburetor over fills / overflows. this could have very negative results as their is effectively an fuel leak on top of the engine spilling down towards the exhaust. some aircraft has prevention to carburetor fuel spills and some don't

how to be sure
I have received instruction from Niren demonstrating the syringe checking method. but I still feel that the absolute best way to make sure if you are the user of the bad batch of floats, is to see them float with your own eyes.
1) gain access to your 912 engine
2) make sure to have proper space underneath the float bowl to remove the bowl.
3) have a big rag handy cause you will spill fuel (not much, about 1/4 cup full)
4) unclip the float bowl by sliding the clip to the one side.
5) slowly pull the float bowl down to clear all the parts inside the float bowl attached to the carb body)
6) once clear, fill the float bowl with some clean fuel
7) Have a good look at the floats they should look like the good float in the attached picture.

Remember when you re install the float bowls it is best to have no fuel in the bowls and be very careful when you position the bowl, you do not want to bend the little arm attached to the carburetor.
If in doubt. refer AVCOM geniuses for elaborate explanations or corrections to my post. :roll:
float 1.jpg
float 2.jpg
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Duck Rogers
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Re: ROTAX 912 series float trouble

Postby Duck Rogers » Thu Feb 19, 2015 5:16 pm

No need for the geniuses to elaborate. You got it right.... vhpy
More info from Rotax on Service Bulletin SB-912-065 (UL) / SB-914-046 (UL), October 06, 2014

Also happens on the Bing 54 carbs for the 2 strokes.......so check those as well from time to time
Airspeed, altitude, or brains....you always need at least two
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Induna
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Re: ROTAX 912 series float trouble

Postby Induna » Fri Feb 20, 2015 8:29 am

you can also follow and older thread about it on Microlighters..

viewtopic.php?f=13&t=23732

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Re: ROTAX 912 series float trouble

Postby Dobbs » Sat Feb 21, 2015 11:27 am

Good post Sout, although I am not sure what the sarcasm is about?

There is a lot of good advice from some very experienced people on Avcom.

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