912 ULS Carburetters

[skippydiesel]

Hi all,

 

My Rotax 912 ULS has 850 trouble free Hobb hrs.

 

Serviced on time every time and complete 5 year rubber replacement up to date. Carb's static & vacuum balanced. Nil oil consumption.

 

Starts & runs perfectly and would appear to be delivering same power and fuel consumption .

 

Started to notice a bit more belly exhaust staining - wondering if engine running a little rich. As I frequently cross the Great Dividing Range, (Tiger country) I like to cruise as high as conditions  allow  - this would exasperate a rich running engine.

 

Q - What would be your collective wisdom on returning carbs to Floods for checking & possible re conditioning?? (tapered needle & seat ware)

 

 

[Blueadventures]

Hi Skippy

 

The jet needle and needle jet do wear.  Floods will do a full carb service for the fair price.  One question is what's the state of the air cleaner? eg newly replaced, cleaned recently eg when you did the 5 years rubber?   If not recently serviced / replaced maybe do that and then see where you are.  Cheers.

 

 

[skippydiesel]

Hi SkippyThe jet needle and needle jet do wear.  Floods will do a full carb service for the fair price.  One question is what's the state of the air cleaner? eg newly replaced, cleaned recently eg when you did the 5 years rubber?   If not recently serviced / replaced maybe do that and then see where you are.  Cheers.

Thanks Blue

 

I was just wondering about other 912 owners - at what hrs did they start to experience a drop in carb performance ??

 

Regarding servicing & 5 year rubber - all complete & up to date .

 

Funny that you mentioned air cleaners/filters - no sooner had I pressed the submit button on my post, I remembered I had replaced my old filters (had started to look a bit tatty) with brand new Flood supplied ones. The new filters looked nice & clean and pre oiled/dressed. I installed them out of the sealed package. Now thinking it might have been better to give them a wash and a fresh dressing befor installation - might try this befor any expensive Flood servicing.

 

 

[Blueadventures]

Maybe if you want find a good experienced 912 carby service person to do it and show you; also if you do this buy from floods the float bracket tool (about $35 a few years back) it screws into where the main jet goes and you'll get the brackets set to specification perfectly every time; quickly and easily. There's nothing like having the carbs 100%. Cheers

 

 

[Downunder]

I believe you start to come "off the needle" and onto the full main jet at about 5000 or so.

 

I believe the needle is more for mid range running but it is  easily adjustable with 4 positions for the "E" clip. Maybe check the clip position and drop the needle one clip?

 

It is easily done with an 11mm socket, phillips and flat screw driver.

 

You can get a size smaller main jet. I think 155 is factory and there are 152's avaliable for 100 hp engines. ( generally 5 minutes to change, only carb bowl removed in situ. 10mm and 11 or 12mm "open enders" needed from memory)

 

The tell tale if running too rich is low egt's. As you climb, you can see it drop away after sbout 4000.....

 

About 800 celcius is about optimum(my opinion)........ 850 is gettting hot........900 is rotax spec max.

 

I like to fly high too. Love the days where you feel like your sliding on glass.

 

The above comments are my opinion only. Yours may differ.....but it's all good!

 

 

[skippydiesel]

I believe you start to come "off the needle" and onto the full main jet at about 5000 or so.I believe the needle is more for mid range running but it is  easily adjustable with 4 positions for the "E" clip. Maybe check the clip position and drop the needle one clip?

 

It is easily done with an 11mm socket, phillips and flat screw driver.

 

You can get a size smaller main jet. I think 155 is factory and there are 152's avaliable for 100 hp engines. ( generally 5 minutes to change, only carb bowl removed in situ. 10mm and 11 or 12mm "open enders" needed from memory)

 

The tell tale if running too rich is low egt's. As you climb, you can see it drop away after sbout 4000.....

 

About 800 celcius is about optimum(my opinion)........ 850 is gettting hot........900 is rotax spec max.

 

I like to fly high too. Love the days where you feel like your sliding on glass.

 

The above comments are my opinion only. Yours may differ.....but it's all good!

Thanks Downunder - great description of what its like to be in a small aircraft, on a clear (smooth) day at 9,500ft - time & movement just seem to stand still, even the sound of the engine becomes muted.

Back to carb stuff - I am sufficiently confident to play around with the carb settings on any land based engine BUT contemplating doing the same thing on an aircraft fills me with trepidation. I will wash & redress my new carb filters - if that doesn't do the trick, I think I will send the carbs off to Floods for assessment/reconditioning.

 

I would still like to get some feedback from the Forum regarding other 912 drivers experience with carburettor wear (Hobb hours, symptom, etc).

 

[Downunder]

I think 155 is factory and there are 152's avaliable for 100 hp engines. ( generally 5 minutes to change, only carb bowl removed in situ. 10mm and 11 or 12mm "open enders" needed from memory)

 All good Skippy.

To correct what I've quoted. Next jet down is 150 and a 10mm and 8mm open enders required. 10mm needs to be thin in cross section (I ground mine down).

 

Maybe see what Flood'recommend for flight at altitude, Jet and needle wise?

 

Personally, if the carbs were still running ok, I would wait for 1000 hrs. The mid point of engine life.

 

Saves you doing them again before 2000 hrs potentially.

 

And I think a full rebuild for both carbs would not be cheap......

 

 

[skippydiesel]

To correct what I've quoted. Next jet down is 150 and a 10mm and 8mm open enders required. 10mm needs to be thin in cross section (I ground mine down).

Are you suggesting a needle & seat replacement can be done with a couple of open ended spanners ??? From distant (probably faulty) memory I thought heat and Lock-tight are involved ??

[Downunder]

No loctite on jet in bowl from what I'm aware. The screw that holds the needle in, is loctited I think. I had no trouble undoing it without heat but it did take a bit of strength.

 

I didn't want to damage the diaphragm with heat. It is quite thin.

 

Older engines had no o-ring above the needle and it did wobble around and wear. Rotax fixed this with an o-ring above the e-clip, under the retaining screw.

 

 

[skippydiesel]

Contacted Floods today - they seem to think it unlikely (but possible) that I have warn needle/seat. They agreed new air filters can be used "straight out of the box"  but support my plan to wash & re "dress" as an elimination action. They mentioned one other possibility - fuel quality. I have been getting my 98 RON from a  nearby BP servo. Servo has recently changed fuel brands - now Caltex. Have no idea if this is significant or not. 

 

The fuel question reminded m, - the first time I noticed this exhaust staining on my aircraft belly was after filling up at Evans Head with no name 95 RON. I added additional fuel, on my trip south, at Armidale Airport Caltex  (98 RON). Could all be coincidence.

 

 

[Blueadventures]

No loctite on jet in bowl from what I'm aware. The screw that holds the needle in, is loctited I think. I had no trouble undoing it without heat but it did take a bit of strength.

I didn't want to damage the diaphragm with heat. It is quite thin.

 

Older engines had no o-ring above the needle and it did wobble around and wear. Rotax fixed this with an o-ring above the e-clip, under the retaining screw.

Blue 243 locate is used. The 'o' only fits the retention screw that has a recess machined into it for the 'o' ring. They are different parts. Just mentioned so people don't just decide to add an 'o' ring into the no 'o' ring models.

 

 

[alf jessup]

Contacted Floods today - they seem to think it unlikely (but possible) that I have warn needle/seat. They agreed new air filters can be used "straight out of the box"  but support my plan to wash & re "dress" as an elimination action. They mentioned one other possibility - fuel quality. I have been getting my 98 RON from a  nearby BP servo. Servo has recently changed fuel brands - now Caltex. Have no idea if this is significant or not. The fuel question reminded m, - the first time I noticed this exhaust staining on my aircraft belly was after filling up at Evans Head with no name 95 RON. I added additional fuel, on my trip south, at Armidale Airport Caltex  (98 RON). Could all be coincidence.

Skippy

There are differences in the blends of fuel from different brands

 

me personally in my 100hp Rotax don’t waste my time on 98 octane as it goes off way to quick compared to 95

 

I only use BP 95 and try to stick to the one brand, I have used 98 when in different locations when 95 is not available.

 

A few brands I never use is Mobil (very sooty fuel I found when used on my BMW bike many years back, fill up on that and go for a ride the back of the exhaust was black)

 

United fuels, for obvious reasons like unknown quality.

 

Shell Vpower is good at eating away at a certain sealant used in a Foxbat fuel tank.

 

My  main one is 95 BP and I will use Caltex of BP is not available, haven’t used Avgas as yet but will if I can’t get 95 easily and obviously used the other brands mentioned if I have no other choice

 

This is only my opinion on experiences I have found over the years

 

Cheers

 

Alf

 

 

[skippydiesel]

Hi Alf,

 

Very interested to hear of your fuel quality observations - I wonder if others have similar observations?

 

Not sure I understand what you mean by "98 octane as it goes off way to quick compared to 95" - Fuel stored in an approved SEALED container is supposed to stay good for at least 12 months. Your aircraft fuel tank is vented, so not sealed, and the fuel contained therein, will deteriorate over time (for me another reason to use  98 RON))

 

I am fully aware that Rotax 912ULS will run quit happily on 95 RON and have used it often when away from home. My reason for using 98 RON is fairly simple ( and may not be completely logical) - I figure (conjecture) that the way fuel is delivered to service stations, is very likely to cause some degree of cross fuel contamination/adulteration (how do you know its actually 98 or 95 ??).  Soooo,if I start with 98 RON, fresh from the pump, it must surely meet or exceed the 95 RON standard. If I start with 95 RON, there is a chance what I put in my aircraft is less than the minimum standard recommended by Rotax.

 

I was using BP and happy with it, but as I said my local servo has changed allegiance and is now a Caltex outlet.

 

Cant comment on your observation regarding Shell V Power - unless it contains or has been contaminated with, ethanol (see my comment above regarding fuel X contamination).

 

On the dreaded ethanol matter - Rotax  912 range is now certified to use fuel blended with up to 10% ethanol (why you would want to is beyond me) but this is not to say non Rotax item like the fuel tank, auxiliary or transfer pumps and fuel lines are also ethanol  compatible.

 

Keep on flying

 

 

[ev17ifly2]

From my limited experience of flying outback NSW we struggled to get any 95 as 98 is stocked at most outlets and from what I was told 95 will soon cease to exist. Got caught out by a supplier at Wilcannia and had to refuel with 91 but because I had around 20 litres in tank it became a cocktail and didn't make much difference. Running AV gas long term in a 912 certainly does when it comes to lead contamination

 

 

[Downunder]

My local BP stopped selling 95. Said it wasn't worth the effort to carry both, as most people who wanted higher octane went to 98 anyway...

 

 

[alf jessup]

Skippy, 

 

98 gets its octane rating from various aromatics blended in

 

Going off I mean by in the plane the octane rating will decrease over time if not used.

 

After a couple of weeks it could be down to say 96, after 6 weeks its rating could be 91, you should see 98 after 6 months or more it looks like honey and smells nothing like fuel

 

Sealed drums may be different as it is not mixing with oxygen.

 

All good if your using it on a regular basis

 

95 has far less additives in it so does not degrade anywhere near as quick

 

91 even better but no good to us with 100hp unless desperate and better shandied with a higher mix

 

 

[alf jessup]

My local BP stopped selling 95. Said it wasn't worth the effort to carry both, as most people who wanted higher octane went to 98 anyway...

Downunder

Glad mine still stocks it

 

Maybe us flyers up here use plenty of it from the same servo

 

 

[ev17ifly2]

According to the Shell data sheet they vary the aromatics in their 95 according to the season. Didn't know that

 

 

[alf jessup]

According to the Shell data sheet they vary the aromatics in their 95 according to the season. Didn't know that

That is so true

thats the problem with automotive grade fuels and oils is that the blends can change week to week as it is not regulated like  aviation fuels and oils which have to done to a certain standard and cannot be changed

 

 

[skippydiesel]

That is so truethats the problem with automotive grade fuels and oils is that the blends can change week to week as it is not regulated like  aviation fuels and oils which have to done to a certain standard and cannot be changed

Are you absolutely sure - I believe that just a few years ago Australia's fuel standards lagged behind much of the developed world. Many car model were not available in Australia, in large part because the fuel we  had available could not be relied upon to be of consistent quality. Under pressure from vehicle manufacturers (trying to reach international emission standards) and international political agreements, on pollution reduction, these standards have been improved. Aviation fuels have always been held to very high & tight standards but surely vehicle manufactures would be up in arms, if their vehicles were unable to meet Australian emission standards, because random fuel quality was making it impossible to do so.

 

The fact that vehicle fuels (particularly diesel) are are seasonally adjusted is nothing new. It has nothing to do with quality but is done to maintain fuel performance in seasonal temperature changes. Australia has relatively small seasonal changes  & consequently small seasonal fuel adjustments - talk to people who live in Canada/Northern USA/Northern Europe, where seasonal temperature variations can be from - 45 to + 45 Centigrade They really do experience large seasonal adjustments to their fuels and seem to get along just fine.

 

 

[skippydiesel]

Skippy, 98 gets its octane rating from various aromatics blended in

 

Going off I mean by in the plane the octane rating will decrease over time if not used.

 

After a couple of weeks it could be down to say 96, after 6 weeks its rating could be 91, you should see 98 after 6 months or more it looks like honey and smells nothing like fuel

 

Sealed drums may be different as it is not mixing with oxygen.

 

All good if your using it on a regular basis

 

95 has far less additives in it so does not degrade anywhere near as quick

 

91 even better but no good to us with 100hp unless desperate and better shandied with a higher mix

It seems to me you are acknowledging the possibility of flying your aircraft with less than the Rotax required 95 RON  (thereby validating my practise) - your 95 RON (if it even was 95 from the pump) will degrade, which means it can only go below 95. On the other hand my 98 RON will also degrade but may only get as low as 95 in a few weeks - a few weeks more it will be at about the level your 95 has now dropped too. Possibility is that we are both flying with the same RON - yours just cost less to degrade than mine.

 

It also troubles me that you might be attempting to use fuel that has been open to atmosphere and is 6 month old - he/she who does that in an aircraft, may not wish to live very long.

 

I am not a chemist, so my tentative opinions are based on what I have heard and read - all fuels "go off" mainly from the volatile fractions being lost as vapour - "evaporating" if you will. This can not happen in a closed container (other very much slower deterioration will occur). All fuels will degrade over time. This will occur more rapidly if the fuel is exposed to the atmosphere (open container) and is influenced by area expose, agitation (which is area) and temperature. I have a sneaking suspicion that sunlight may also be factor - hence opaque containers stored in dark places seems to be the norm. The small "breather" vent on  most fuel tanks will allow the volatile fractions to escape but not as quickly as say the tank cap being left off (surface area exposed to atmosphere). In theory fuel tanks should be kept full (minimising surface area evaporation and water condensation development) or near empty, so that fresh fuel can be added befor each flight - practicality is another thing.

 

 

[alf jessup]

Skippydiesel

 

I can assure you my fuel does not degrade very much at all my plane does not sit idle for too long

 

I average over 100 hours a year for the last 14 years

 

145 last year alone

 

All I was saying is 98 degrades at a much faster rate than 95 does

 

And no I don’t use 6 month old fuel at all I am basing that on aircraft that have seen that had not flown in 6 months where the fuel system was drained and replenished with fresh fuel

 

6 month old 91 still smells like petrol

 

6 month old 98 sure doesn’t, 95 I haven’t come across any 6 month old yet but when I do I’ll let you know

 

 

[dsam]

I “hangar” my Eurofox in a trailer with wings folded back. My wing tanks need to be well under half full when stored this way, or I can sometimes get fuel leakage out the top vents.

 

I always buy fresh Shell 98 from a high volume retailer on my way to the airfield. I’m told that in Victoria they don’t use ethanol in their 98.  I’ve had no issues in the last 6 years doing this. 

 

 

[Camel]

I only use 95, as I have had problems with 98 and it has left contamination in the float bowl of a stationary engine I used it in !  I would inspect in float bowls for any contamination, it is like a varnish appearance ! I definitely would not use 98 Ron !  I'm told that 95 does not have additives but 98 does have additives to boost octane rating so correct me if I'm wrong on this ! 

 

 

[Kiwi]

Check out THIS from BP "EXAMPLE OF HOW PETROL CHANGES WHEN STORED IN FUEL TANK"

 

Kiwi