912 ULS

[Garry_Smith]

An incident with a Rotax 912 ULS Bing carburetor

 

 

            On turning on the fuel in my plane, even without the electric fuel pump on, fuel was pouring from the bottom of the motor enclosure, it was found that the co-pilots carburetor was literally pouring out of the bottom of the fuel bowl though a hole about 1mm in diameter.

 

On the removal of the bowl, it was found that the outer float was laying over in the bowl along with its holding pin.

 

On further testing, it was found that the fuel pump could keep the bowl full of fuel and the float working even though the fuel was pouring out of the hole in the bottom of the carburettor. The problem was fixed, but, is this a design fault? If the hole didn’t go right through the carburetor bowl and the same thing happened, then the fuel then would not have been able to escape and become a fire hazard. We were lucky it was found before flight.

 

I have a feeling that this has been happening for a while as sometimes when I did the pre-takeoff checks, I would wipe my finger under the co-pilots side carburettor and there was an orangey fuel stain, consequently, I have taken the bowl off to have a look at the bowl seal but only to find nothing obvious. The pin must have been loose but not loose enough to fall out of it’s mounting hole.

 

 

 

[facthunter]

I've always felt this is not really an "aircraft standard" carburetter. There have been issues with the float sinking but that's not your problem in this instance. Use the right float and be very CAREFUL assembling it, is all I can suggest. Not really that satisfactory is it? Nev

 

 

[Blueadventures]

An incident with a Rotax 912 ULS Bing carburetor

            On turning on the fuel in my plane, even without the electric fuel pump on, fuel was pouring from the bottom of the motor enclosure, it was found that the co-pilots carburetor was literally pouring out of the bottom of the fuel bowl though a hole about 1mm in diameter.

 

On the removal of the bowl, it was found that the outer float was laying over in the bowl along with its holding pin.

 

On further testing, it was found that the fuel pump could keep the bowl full of fuel and the float working even though the fuel was pouring out of the hole in the bottom of the carburettor. The problem was fixed, but, is this a design fault? If the hole didn’t go right through the carburetor bowl and the same thing happened, then the fuel then would not have been able to escape and become a fire hazard. We were lucky it was found before flight.

 

I have a feeling that this has been happening for a while as sometimes when I did the pre-takeoff checks, I would wipe my finger under the co-pilots side carburettor and there was an orangey fuel stain, consequently, I have taken the bowl off to have a look at the bowl seal but only to find nothing obvious. The pin must have been loose but not loose enough to fall out of it’s mounting hole.

 

[ATTACH]42012[/ATTACH] [ATTACH]42013[/ATTACH] [ATTACH]42014[/ATTACH]

 

Thanks for sharing.   Would be keen to hear what Floods (agent) and RAA say about this.  Definately something to look out for.  Cheers.

 

 

[Kyle Communications]

Also the fuel float needles can also bleed fuel into the engine if you have wing tanks and leave your fuel tap on..it will fill your engine up. They get crap on them from old fuel and end up not sealing when the bowls are full

 

 

[skippydiesel]

Hi Kyle,

 

Alarming incident - I will certainly check for  float "pin" security at the next service.

 

It may  or not be relevant but how about giving us some more information on your ULS - age, hours AND what remedial action have you taken ???

 

 

[Downunder]

Off on another tangent, but still relating to 912 carbs.

 

I noticed my (metering) needle has movement of about 1mm in and out of it's housing.

 

It has the o ring above the "E" clip. I would have thought the o ring should be snug against the clip and limit movement.

 

The securing screw is tight and all looks fine and undamaged.

 

Anyone else find or notice this?

 

 

[Kyle Communications]

Hi Kyle,

 

Alarming incident - I will certainly check for  float "pin" security at the next service.

 

It may  or not be relevant but how about giving us some more information on your ULS - age, hours AND what remedial action have you taken ???

 

 

 

Yes it was seeing about 10 litres of petrol went into the engine. The way you know is when you turn the prop over and its like a hydraulic lock and the prop doesnt want to move. Then it does then all of a sudden a whole heap of liquid comes out of the oil tank because the cap was off to check the oil. I immediately dumped all the hoses off the engine and drained it all then put new oil in and filter on. left the plugs out and spun the engine over with the new oil then drained all that oil then did the whole process again again until the engine was totally cleaned out. Then reloaded it all again and started the engine and it runs smooth as and no issues. Imagine if you jumped in and tried to start it first without doing the normal checks first. 

 

The needles that the floats work on were the issue. The carbs were stripped and cleaned there was a film over everything in the carbs. its the crap 98 fuel now. I now use a fuel stabiliser in all my fuel especially if you dont fly regularly. This film was making those needles not seal properly. I always turn the fuel off at my tanks as its a high wing. But for some reason I didnt turn one off and thats how I found the issue but I hadnt flown or started the engine for about 5 weeks so it took a long time to drain all that fuel into the engine by gravity. The issue is that fuel goes off really quickly now especially the higher octane stuff

 

Downunder

 

The main needles get worn quite quickly if you look at them under a magnifing glass you most likely will see the wear. I have replaced all the needles in my carbs as a matter of course in the 3 engines I have here. Even the 150hr engine shows some wear the 340hr engine shows a lot more wear and the 2000 hr engine is well worn

 

 

[skippydiesel]

Yeh! there seems to be quit a lot of concern about "stale" fuel especially 98 RON.

 

I try not to keep large quantities of fuel in my (vented) aircraft tank when not flying. I fuel up before most flights with fresh fuel from a sealed plastic jerry can.

 

Never had a problem, so live in hope that this approach is diluting ("shandying") any deterioration that may have occurred.

 

 

[Kyle Communications]

Well I learnt my lesson. I am now using stabiliser. I put it in each 20litre I fill up at the garage so its always in the tank. This particular one I use is also a cleaner as well so it will degunk your system the more you use it.

 

I was always aware of the stale fuel issue and if I hadnt used the aircraft for 6 weeks I would dump the fuel back into containers and feed it to the Mrs car and put new fuel into the aircraft. Well this obviously doesnt work. So now with this stabiliser hopefully it should be better. Of course the solution is to fly every week or so but the way my life works thats not always anywhere near possible

 

 

[skippydiesel]

There was a very good conversation on this topic a while back - one of the fuel companies has done quite a bit of research into fuel storage/degrading.

 

In short - if you keep your 98 RON in sealed/airtight containers that are 75% or better full, the fuel will remain in good condition for a long period (from memory 9 months+) that's why I use HD plastic jerry cans . If the can expands /contracts with daily temp changes its well sealed - fuel OK. Converse may be true.

 

Also - the actual effect of aged fuel, is to slightly raise the RON (counterintuitive I know) but the loss of other volatiles, may have a negative impact on the starting qualities of the fuel. Once running should be OK.

 

AND

 

The shandying/mixing of a significant amount (relative) of fresh fuel into old, will almost completely "make good" all the qualities of the whole - I would guess that this may depend on the actual time the old fuel is open to atmosphere.

 

Sooo - rather than add "stuff" to your fuel, get some plastic jerry cans from Bunnings Aerospace (had mine for about 6 years, $19 each from memory) - add fresh fuel before first flight of the day. Simples !

 

 

[Kyle Communications]

I used to do all of what you said...put a lot more fuel into the tanks to blend it etc..did all of that and still got the issue. I keep fuel in plastic containers that are sealed and swell as well. I do this up at my farm for the quads etc and havent had too much drama as yet. But I think because the breathers on the fuel tanks are always venting as you can see it distorting the air if you look coming out of the breathers when in the hangar.

 

I read if you keep the fuel with about 1 to 2 PSI pressue on it then the volitiles and octane do not degrade much at all. my plan was to use 60litre drums and make a fuel storgae/pump setup fr the aircraft. Just decant the new fuel int the drums. I have a "Tanami" pump which is just a cap that fits into the metal drum with a no return air valve and you pressurize through it to pump the fuel out. Then you keep 2 psi or so in the drum and this keeps the fuel fresh. I havent got abound to making this fuel rig up although I have the drums and the Tanami. I will also make one for up at the farm as well. But the crap in the system doesnt lie so it must be cause by the fuel and its never been more than 6 weeks ever that I havent filled or drained the tanks and started the engine

 

I only use 98 in the quads and in the aircraft.

 

 

[skippydiesel]

I used to do all of what you said...put a lot more fuel into the tanks to blend it etc..did all of that and still got the issue. I keep fuel in plastic containers that are sealed and swell as well. I do this up at my farm for the quads etc and havent had too much drama as yet. But I think because the breathers on the fuel tanks are always venting as you can see it distorting the air if you look coming out of the breathers when in the hangar.

 

I read if you keep the fuel with about 1 to 2 PSI pressue on it then the volitiles and octane do not degrade much at all. my plan was to use 60litre drums and make a fuel storgae/pump setup fr the aircraft. Just decant the new fuel int the drums. I have a "Tanami" pump which is just a cap that fits into the metal drum with a no return air valve and you pressurize through it to pump the fuel out. Then you keep 2 psi or so in the drum and this keeps the fuel fresh. I havent got abound to making this fuel rig up although I have the drums and the Tanami. I will also make one for up at the farm as well. But the crap in the system doesnt lie so it must be cause by the fuel and its never been more than 6 weeks ever that I havent filled or drained the tanks and started the engine

 

I only use 98 in the quads and in the aircraft.

 

Kyle - I dont want to suggest I am an expert on this but it seems to me that you may be over complicating the problem.

 

To the best of my knowledge all simple aircraft (RAA/GA) use vented fuel tanks - that is they are open to atmosphere and therefore subject to fuel volatiles evaporation/gassing off (the distorted air)

 

Over many years, I have had no problems with fuel storage in 20 L plastic fuel cans, that are filled to exactly 20 L for easy fuel calculation AND minimal air space above fuel (75% + rule).

 

The pressure in a sealed fuel container is probably going to exceed the 1-2 psi (particularly on a hot day) so I can't see the benefit in pre pressurising.

 

I like the idea of a Tanami system but again it meas running an extra (air) pump (you may already have air pressure on tap). I have made up a perfectly functional 12 V transfer pump for about $80 (not counting all the failed attempts) that works very well for me at or away from home.

 

I dont get any "crap" in my system - could be I get my fuel from high turnover servo's - may also be that I filter ( home modified funnel) all fuel going into my aircrafts tank - I am also up to date with my rubber (all fuel lines) replacement and I use what I believe is a quality fuel hose  (Gates Barricade FI line) so no bits of hose in the fuel - by using plastic fuel cans I dont get any metal/paint/rust particles in my fuel and so far no sign of water.

 

 

[Kyle Communications]

No different to me. I get my fuel and its BP usually as that is the best quality 98. I have extra filters inline in my fuel system high quality metal cases one and a gascolator and all EFI teflon style barrier fuel hose through out the aircraft all changed every 5 years and not one milli litre of fuel goes into my tanks without going through the Mr Filter filter or what ever its called that everyone uses to strain their fuel with the water trap in it. The only reason for the tanami is I am lazy so this way I can keep a reasonable amount of fuel in the hangar safely in metal drums and it will last a long time this way so I can just fill it up seeing you can only fill up 20ltr drums at a time here in the big smoke not a 44 gal drum at the servo like in country areas. So its a real pain filling and humping 6 fuel containers in and out of the servo so much easier to take one or 2 and keep  the fuel rig always topped up.

 

I am not doing anything unusual at all but the gunge was in the fuel system and I thought I was taking all reasonable steps to be carefull with my fuel quality...I only made he comment to make others aware that they COULD also get this issue

 

 

[facthunter]

Fuel will go off due to bacterial action and it really stinks and makes things you don't need in your fuel system. Jet A1 has additives to stop it but bit still ends up in filters. Some tanks get it and some don't.   The best thing to do with OFF fuel is kill weeds with it . Nev

 

 

[skippydiesel]

No different to me. I get my fuel and its BP usually as that is the best quality 98. I have extra filters inline in my fuel system high quality metal cases one and a gascolator and all EFI teflon style barrier fuel hose through out the aircraft all changed every 5 years and not one milli litre of fuel goes into my tanks without going through the Mr Filter filter or what ever its called that everyone uses to strain their fuel with the water trap in it. The only reason for the tanami is I am lazy so this way I can keep a reasonable amount of fuel in the hangar safely in metal drums and it will last a long time this way so I can just fill it up seeing you can only fill up 20ltr drums at a time here in the big smoke not a 44 gal drum at the servo like in country areas. So its a real pain filling and humping 6 fuel containers in and out of the servo so much easier to take one or 2 and keep  the fuel rig always topped up.

 

I am not doing anything unusual at all but the gunge was in the fuel system and I thought I was taking all reasonable steps to be carefull with my fuel quality...I only made he comment to make others aware that they COULD also get this issue

 

It's a mystery Kyle - I use Caltex or Ampol, BP is too far away.  I have 6 x 20 L & find them quite easy to move about - just slide them in /out of ute.

 

Never tried to purchase more than 100 L of 98 RON so unaware of any limit.

 

Aside from the aforementioned filter funnel -  I  have one inline filter on each delivery line (main, aux & reserve). From an erlier post by me;

 

Hengst In Line Gauze Fuel Filters

 

Part No - H103 WK (90 degree fitting one end) 

 

Part No - H102WK ( straight)

 

Both filters have:

 

8mm inlet/outlet spigots

 

An overall width of just 36mm

 

Overall length of 103 mm

 

Hengst claim a fuel filtration capacity of ≥ 2 µm (0.002 mm)

 

I have found these filters to have the following excellent features:

 

• Clear body - for easy condition check
   
  

 

 

 

• Very strong - in normal use it is just about impossible to break these beauties
   
  

 

 

 

• Light weight - why add grams when you don't need to.
   
  

 

 

 

• Leak free - unless damaged somehow, the fully sealed body cannot leak. I use good quality fuel injection hose clamps to ensure the push into hose fit does not leak or pull out.
   
  

 

 

 

• Large Filter Area - very low fuel flow restriction/ less stress on pumps/ less likely your engine will experience total fuel starvation should contaminated fuel be inadvertently introduced to your system.
   
  

 

 

 

• Long service life - assuming you are only using clean fuel in the first instance, these filter need only be replaced "on condition" however I would be inclined to replace them when you replace your fuel hoses.
   
  

 

 

 

• Reusable - for the most part, with care, some carbi clean (or similar) & a little air pressure, most contamination of the filter can be removed. Why bother, they are so cheap, just replace them.
   
  

 

 

 

• Cheap - I always carry spares in the unlikely event that I need to do a "field" replacement.
   
  

 

These filters are commonly fitted, as pre filters,  to European diesels up to about 3.2 L

 

• German Designed - made in Israel these filters are beautifully engineered and presented.