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schedule for carburetor overhaul?

  • kdismukes
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5 years 8 months ago #4589 by kdismukes
schedule for carburetor overhaul? was created by kdismukes
As i read the maintenance manuals for the 912uls, the carbs should be disassembled and inspected every 200 hours, but replacement of components (including rubber components) is on condition, not at any set time. Is this correct?

thanks,

Key

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5 years 8 months ago #4590 by bravo23c
Replied by bravo23c on topic schedule for carburetor overhaul?
Hi, I believe the 5 yr rubber replacement recommendation applies to the carb o-rings , gaskets and diaphragms.

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5 years 8 months ago #4591 by kdismukes
Replied by kdismukes on topic schedule for carburetor overhaul?
Thanks--i needed that info for tomorrow!
key

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5 years 8 months ago #4593 by billmartin
Replied by billmartin on topic schedule for carburetor overhaul?
Key,

Kevin is right. All rubber components in the engine and carbs should be replaced at five year intervals. This replacement does not relate to engine hours but is based on engine age.

Bill.

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5 years 8 months ago - 5 years 8 months ago #4614 by Skyranger2
Replied by Skyranger2 on topic schedule for carburetor overhaul?
I'm not an A&P or greatly Rotax experienced, so although I'm a decent mechanic, take what I say next with a grain of salt:

On the Rotax and indeed the whole aircraft seems to me we should always be balancing between
"an ounce of prevention is worth a pound of cure" and doing the sort of proactive maintainance and replacements Rotax recomends,
AND ON THE OTHER HAND
take seriously the "It it ain't broke, don't fix it."
Talk to any honest A&P and I bet they have lots of stories of someone, or even they, taking apart some subsystem that was working properly, putting it back together, and having problems with it.

So one thing to think about in doing "preventive overhaul" -- particularly if it's expensive or challenging -- be it on carbs or anything is this:
If you DON'T do the preventive overhaul and it turns out it REALLY was needed, what's the worst that can happen? Could it (a) cause a serious accident and/or (b) cause more complicated or costly repairs due to the neglect? OR would it not serious? Could you just wait until that subsystem shows symptoms of failure or sub-optimal function?

In short, in my opinion, and in the opinion of several far-more-expert-than-me A&P folks, there are some things, even on ADs, that it is better, and safe, to leave alone and wait until they actually fail or show symptom of failure, if ever, rather than doing proactive maintainance or replacement.

Of course there are places that it is foolish, dangerous, and illegal to neglect.
And in some cases, especially with standard category aircraft where it's illegal to defer maintainence. But if it's not one of those cases ........

In the case of a carb overhaul that is deffered longer than officially recommended or even longer than it should be for functionality, IMO the worst that's likely will happen is that you will get some loss of power and loss of fuel efficiency.

If your plugs are reading right (not indicating you're running too rich nor too hot/lean) and you're getting normal power and normal fuel consumption, idle and cruise is smooth, your carbs are working right, and in my opinion personallyI wouldn't touch them unless you just have TOO much free time on your hands :unsure: .... except take off the bowls to check for sediment. If you take the bowls off it's a good idea to have at hand spare new bowl gaskets BEFORE you remove them.

We periodically put a bottle of NAPA carb cleaner through our fuel tank. $3 per bottle.

My very unofficial two cents.

Al
Last edit: 5 years 8 months ago by Skyranger2. Reason: Adding two relevant paragraphs/thoughts

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5 years 8 months ago #4619 by mainairmark
Replied by mainairmark on topic schedule for carburetor overhaul?
Hi Al

I hear what you are saying, but I would suggest the carbs are serviced at the recommended intervals.

You need to strip the carb to see if the needle is showing signs of wear. On the two strokes the retaining clip used to cut the needle in half and the needle would drop into the needle jet, causing and engine failure, even though ten seconds earlier it was running perfectly.

The float hinges wear through with time and vibration where they pivot on the hinge pin. I have seen these break off and the needle valve falls out causing an engine failure.

Float can disintegrate and float pins wear, some more than others, and the thing is every aircraft is different. They have different levels of vibrations and they resonate at different frequencies which means that one aircraft might last forever and another will wear after a couple of hundred hours, or less.

Stick to what the manufacturers recommend, they are speaking from experience.

Mark

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5 years 8 months ago #4624 by Skyranger2
Replied by Skyranger2 on topic schedule for carburetor overhaul?
Hi Mark,
I hear what you're saying too.
You clearly know carb issues better than I do. Especially the two cycle.
And unless you turn out to be the guy who gets hurt BECAUSE someone did preventative e maintainence and did it wrong (some NTSB findings on fatal crashes HAVe turned out that way..really) I support your better safe than sorry stance.
There are many things I have done and will do on our plane in that spirit.
And I DO value reading when rotax says about when to do what... If for no other reason that whenRotax says rebuild system X at 600 hours it gives me confidence that it's very unlikely to need attention any SOONER that that . ;)


That said, although I would be very unhappy to try to limp to a landing on one carb, it's still not in the class of risk of, say, ignoring a rattle in the reduction gearbox, a fuel line clearly showing its age,etc.
And as for "Stick to what the manufacturers recommend, they are speaking from experience.".....
Yes Rotax has brlllliant careful engineers looking at this stuff making these calls and recommendations. But Remember they are also speaking from a liability stance: Tha is the attitude that "we'll never be sued for telling people they have to service the carbs every 200 hours even though
We believe it,s extremely unlikely that's needed in less Tha 1000 hours...but let even one of our 30,000 owners claim he got hurt because his accident might have bee prevented by rebuild at 200 and we could be in a multimillion dollar lawsiuit." And not meaning to be cynical ... There IS a nice profit margin in selling complete rubber seal/gasket/parts kits if you can get 30,000+ owners to replace every single rubber part every 5 years despite the fact that some are under use,temperature, environment, and total hours that age those components differently.... And the risks of deterioration of some rubber parts would not be high risk.

I just don,t think there's anyway of getting around the reality that "an ounce of prevention is worth around or cure" and "better safe than sorry" AND "if it ain't't broke don,t fix it" all have I validity and need constant judgement calls...even in the face of Rotax guidelines.

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5 years 8 months ago #4625 by mainairmark
Replied by mainairmark on topic schedule for carburetor overhaul?
Al

The two carbs aren't there as a back up. If one had a problem the chances are you won't be limping to your landing site, your engine will shake it's self to pieces. It won't run on one carb.

If you don't know how to do something on the engine, don't do it yourself or bury your head in the sand and say

" well it will probably be OK, it is just Rotax trying to cover their arse or make some more money out of me",

get someone who knows what they are doing to sort it.

You owe it to your passengers to be responsible and to listen and do what people with a lot more experience and understanding recommend i.e.Rotax.

Through a little experience, I am with "correct preventative maintenance" all the way.

Good luck,

Mark

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5 years 7 months ago #4646 by Skyranger2
Replied by Skyranger2 on topic schedule for carburetor overhaul?
Good luck to you too, Mark

By the way.... Mind telling us approx what the each Bing carb rebuild kit cost you when you did yours?
I think I may remember seeing each was over $400. Surprising as I'm pretty sure last time I did a rebuild of a carb (was a two barrel one on a auto) the kit was under $40. The large difference in price , IIRR, was puzzling. Did you have to use a full kit or just selected parts??

Al

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5 years 7 months ago - 5 years 7 months ago #4647 by Roger Lee
Replied by Roger Lee on topic schedule for carburetor overhaul?
There are different carb rebuild kits from different Rotax distributors. They unfortunately are not standardized. You may get a kit of just "O" rings for around $40 from one or a kit with everything inside the carb (more or less) for around $350. These kits are for two carbs. A good complete kit from CPS with everything except the floats is $255. There is nothing in writing in the Rotax manual for a mandatory carb overhaul, just the rubber parts. I am a believer in carb overhauls at some point. I do them on a regular basis in my shop that are sent from all over the US. The overhaul doesn't take long, is straight forward and just needs a little attention to detail to make the carb brand new again.Carb parts are in motion inside and do wear. "O" rings do crack and split and get flattened out and then can leak (#1 issue). Metal tolerances on moving parts do wear. If you let carbs sit for long periods of time with fuel in them they will start to clog especially the very tiny offices in the idle jet system.
I just did a set yesterday where someone had a bowl gasket leak and used silicone to try and seal it instead of replacing the bowl gasket. That silicone migrated throughout the carb and caused restriction issues. Never use silicone around your fuel system, it is not compatible.

If you call a distributor and order a carb rebuild kit ask what is included. Kits are a nice way to go, but if you needed just a certain part it can be ordered that way.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last edit: 5 years 7 months ago by Roger Lee.
The following user(s) said Thank You: Skyranger2

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5 years 7 months ago - 5 years 7 months ago #4648 by Skyranger2
Replied by Skyranger2 on topic schedule for carburetor overhaul?
Much thanks for the very usefull info!

You wrote --
"I just did a set yesterday where someone had a bowl gasket leak and used silicone to try and seal it instead of replacing the bowl gasket. That silicone migrated throughout the carb and caused restriction issues. Never use silicone around your fuel system, it is not compatible."

That's an interesting coincidence.
A month ago we pulled the bowls on our carbs for routine check. Found the same issue you described from previous owner having used clear silicon caulk (or maybe it was gasket sealer) apparently to address the issue of a cracked bowl gasket on one side instead of replacing the gasket. 
I'm sure he thought his fix had worked OK because the bowl was not leaking.
In our case the silicon had not yet caused problems but it was very clear that small gobs of the silicon were at serious risk of breaking free and floating elsewhere in the carb causing problems.
FWIW, IMHO putting a tiny bit .... very thin layer .... of silicon _grease_ on of surface of gasket (helps to get gasket stay seated in groove while seating bowl and presumably better seal) is acceptable. (Not as a substitute for replacing a gasket.) Your thoughts on that?
Also curious if you have any opinion of the third party silicon rubber bowl gaskets, which some claim are superior to the standard Bing cork ones?

...................

Contrary to the impression my exchange with Mark may have left, I too am a believer in as you say carb overhauls at some point. More so obviously on an aircraft than, say, an ATV.
Just don't fully buy into the idea that anyone who doesn't do everything Rotax recommends and do it on the Rotax recommended tach hours is irresponsible and incurring significant or necessarily any risk.
Do I take it right that you aren't hard core about "do it every 200 hours" and more likely to make your call on a case by case basis?


I assume that, unlike whe just checking the bowls and r&r bowl gaskets, the carbs have be completely removed from the engine, and tha in turn means we'd expect to have to do a complete mechanical and dynamic carb sync after reinstalling them. Right?

Al
Last edit: 5 years 7 months ago by Skyranger2. Reason: Added last tw lines about required re-sync.

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5 years 7 months ago #4650 by Roger Lee
Replied by Roger Lee on topic schedule for carburetor overhaul?
Hi Al,

If you use anything to dress an "O" ring or gasket around the fuel or oil system then use White Lithium Grease.It is compatible with fuel and oil and when it gets hot or mixed it just turns back to an oil more or less and blends with the fuel or oil. I do rub some of my "O" rings with it and I have done so at times on some gaskets. No need to glob it on just rub it on or in and don't leave any globs. It will also help some "O" rings to seat into their respective position too and instead of a dry pushed in fit that sometimes can cause an "O" ring to roll or flatten out of place. Some discretion here is warranted and it isn't for everything.

In the case of a leaky carb bowl gasket just replace them. I always keep some on hand because bowl gasket leaks do happen.

Her's another tip. If you need to pull the carb bowl off many times the drip tray or something else is in the way. You can remove the 4 screws that secure the air intake on the affected side and this will allow you to lift the carb high enough to pull the bowl to remove it and dump bowl debris or replace the gasket. Just make sure not to drop anything down that air intake hole or it will cause damage to a valve. Then torque the 4 screws back down to 90 in/lbs.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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5 years 7 months ago - 5 years 7 months ago #4658 by mainairmark
Replied by mainairmark on topic schedule for carburetor overhaul?
"speak of the devil"

Some one came up to me yesterday when I was between lessons. He had just landed and said his engine was running rough on final and when he landed the engine ran very rough and then stopped. He restarted it but it wouldn't tick over, as it would run rough and then stop.

The tray under his carb was wet with fuel and so we removed the carb and float chamber. I new straight away what the problem was, and with the correct maintenance it would have been avoided.

This is what we found.



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Last edit: 5 years 7 months ago by mainairmark.
The following user(s) said Thank You: Gyrochook.

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6 months 5 days ago #18008 by Wang Shu
Replied by Wang Shu on topic schedule for carburetor overhaul?
kindly guide in detail of CARBURETOR RUBBER parts that required to change After 05 years of times?
list required please

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6 months 2 days ago #18030 by Leopold
Replied by Leopold on topic schedule for carburetor overhaul?
David,
I would suggest to call Lockwood or Roger.

Al and Roger,
I just signed up to the forum. Many thanks for your (already 5 years old) thoughtful explanations! I have learned a lot from your, Roger, most competent contributions (here and at matronics) - and from Mike Busch, however. I must admit I generally tend somewhat more to the approach of Mike Busch (who gives more emphasis to: 'don't fix it if it ain't broke'). I myself may legally do so. My 80 hp Rotax 912 runs since about 8 years/1400 hrs in a German ultralight and in this legal framework maintenance is at the end of the day owner responsibility. I do take maintenance -very- seriously and spend quite some time on it. Many things I would never do myself. But after more than 30 years of aircraft ownership I consider myself a fairly experianced amateur with an appropriate toolbox.

My experiance on Bing 64 carburators: I take always -one- apart every 100 hrs and inspect it. The carbs deteriorate slowly over the years: Slight traces of vibration wear, I had to replace both needle valves after 700 hrs. Otherwise they never gave me any trouble at all and I did not do the 200 hrs. carb overhaul. I fly exclusively with autofuel, 10% alcohol.

Leopold

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6 months 8 hours ago #18041 by jiott
Replied by jiott on topic schedule for carburetor overhaul?
I fly with auto fuel-no alcohol and don't plan to disassemble the carbs until 5 year rubber replacement, which for me will be about 800+ hours. As long as they are running perfectly I tend to go along with Mike Busch also-Don't fix what isn't broke. I have two friends with 912uls who haven't disassembled the carbs for over 1000 hours, and 700 hours. I do remove the bowls every annual to check for dirt and good floats, and carefully inspect the sockets externally.

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