Cleaning carbies/looking for blockages.. tips?

[skippydiesel]

1 hour ago, danny_galaga said:

Is there a normal overhaul period of hours or years for carbies like there is for rubber hose replacement?

Not that I am aware of.

[RFguy]

be sure to remove the varnish off any (rotating) shafts, also.  replacing o rings etc, one can forget cleaning the things that run through them .

[facthunter]

With O rings and such  I reckon I'd rebuild those carbs at least every 3 years since they are not on a motorbike anymore.  Nev

[danny_galaga]

On 26/09/2023 at 6:20 PM, Blueadventures said:

HI Danny  If your good to clean carby's; you can check them at the field; allow 3 to 4 hours.  Any dismantle of the fuel route components would require at the very minimum the 'O' rings that fit the idle jet, idle mixture needle and the mixing tube (Diagram 'O' rings #9 x four and #5 x two 'O' rings) as you are doing two carbs.  That will allow checking the major fuel route and metering but not include the enrichers.  This will ensure you can reassemble the same day and test.  My recommendation is to fit a carb kit to each carb.

It's taken me 4 years to build a kit that apparently should only take 6 weeks. Imma need more than 3 or 4 hours 😄

 

If mechanically everything is fine, I notice there is an O ring and gasket only 'sub' kit available. That might be a good thing to go with, provided the diaphragms still look good. What do you think?

 

https://www.aircraftspruce.com/catalog/eppages/bingdualcarb15-09421.php?clickkey=10575489

[onetrack]

Replace the diaphragms, even if they look O.K. - they're the major rubberised wearing items in a carby.

[danny_galaga]

21 minutes ago, onetrack said:

Replace the diaphragms, even if they look O.K. - they're the major rubberised wearing items in a carby.

Ok. will do. So THEN my next conundrum is do I get this kit, which does two carbies, but has no floats or float lever thingies or springs etc:

 

https://www.aircraftspruce.com/catalog/eppages/15-05914.php

 

or do I go with two of these, which has everything, but adds up to a hell of a lot more:

 

https://www.leadingedgeairfoils.com/rotax-engines-parts/genuine-rotax-parts/4-stroke-parts-912-914-series/912-914-series-parts/carburetors-fuel-system/overhaul-kit-carburetor-912-912uls.html

 

I guess I have to make a careful assessment of wear and tear first...

[BrendAn]

2 hours ago, danny_galaga said:

Ok. will do. So THEN my next conundrum is do I get this kit, which does two carbies, but has no floats or float lever thingies or springs etc:

 

https://www.aircraftspruce.com/catalog/eppages/15-05914.php

 

or do I go with two of these, which has everything, but adds up to a hell of a lot more:

 

https://www.leadingedgeairfoils.com/rotax-engines-parts/genuine-rotax-parts/4-stroke-parts-912-914-series/912-914-series-parts/carburetors-fuel-system/overhaul-kit-carburetor-912-912uls.html

 

I guess I have to make a careful assessment of wear and tear first...

They look like excellent kits. Got everything In them. Floats are the expensive part .

[dlegg]

Like you say...".I guess I have to make a careful assessment of wear and tear first..". I'm a big fan of correctly identifying the fault first, before having a big collection of un needed expensive spare parts.

[skippydiesel]

Rotax recommend a "rubber" replacement every 5 years - little to be gained by doing this at 2-3 years, other than a lighter wallet.

 

Be careful of "kits" that supply parts that you don't need - weigh your floats (the expensive bit) befog commiting to new ones. Rotax have the weighing procedure & max  weight, in their maintenance manual. Jewellers scales (for weighing floats) are not very expensive.

[skippydiesel]

5 hours ago, RFguy said:

be sure to remove the varnish off any (rotating) shafts, also.  replacing o rings etc, one can forget cleaning the things that run through them .

Word of caution: I just found out (on the Rotax Owners Forum) that the carby's have an epoxy coating(looks a bit like varnish) - this should not be removed

[BrendAn]

22 minutes ago, skippydiesel said:

Rotax recommend a "rubber" replacement every 5 years - little to be gained by doing this at 2-3 years, other than a lighter wallet.

 

Be careful of "kits" that supply parts that you don't need - weigh your floats (the expensive bit) befog commiting to new ones. Rotax have the weighing procedure & max  weight, in their maintenance manual. Jewellers scales (for weighing floats) are not very expensive.

You could look at it another way and say give the carbs a full kit and new floats for piece of mind. A fairly small investment compared to what he is spending building the aircraft.

Older 912s can have 2 types of float . 1 type should be replaced  , I think it's called a b type but someone will know.  

[facthunter]

I don't think rubber replacement would relate to carburettor's internals. The float type is like an AD..   Nev

[skippydiesel]

13 hours ago, BrendAn said:

You could look at it another way and say give the carbs a full kit and new floats for piece of mind. A fairly small investment compared to what he is spending building the aircraft.

Older 912s can have 2 types of float . 1 type should be replaced  , I think it's called a b type but someone will know.  

The rubber replacement isn't cheap , is conservative at 5 years & does not usually include the floats. My last 912ULS was a 2000 build - the floats supplied at that time would seem to have had an indefinite life span. Younger variants had fuel absorption/reduced floatation problems. The latest is hopefully back in the indefinite lifespan. The test is simple, dry & weigh-

 

From Rotax Maintenance Manual Line: 12-20-00, Page 36, CHECK THE WEIGHT OF FLOATS

 

"Step Procedure 1 Let the floats dry for 1-2 minutes, then weigh the floats. Only weigh dry floats. 2 Check the weight of all affected floats using a calibrated scale. Measuring tolerance of the scale: max. 0.1 grams. 3 The results of the measurement must be documented in the maintenance records. The max. allowable weight (of both floats together) is 7 grams. ATTENTION Replace all floats which exceed the max. weight"

10 minutes ago, facthunter said:

I don't think rubber replacement would relate to carburettor's internals. ....   Nev

It does.

[BrendAn]

9 minutes ago, skippydiesel said:

The rubber replacement isn't cheap , is conservative at 5 years & does not usually include the floats. My last 912ULS was a 2000 build - the floats supplied at that time would seem to have had an indefinite life span. Younger variants had fuel absorption/reduced floatation problems. The latest is hopefully back in the indefinite lifespan. The test is simple, dry & weigh-

 

From Rotax Maintenance Manual Line: 12-20-00, Page 36, CHECK THE WEIGHT OF FLOATS

 

"Step Procedure 1 Let the floats dry for 1-2 minutes, then weigh the floats. Only weigh dry floats. 2 Check the weight of all affected floats using a calibrated scale. Measuring tolerance of the scale: max. 0.1 grams. 3 The results of the measurement must be documented in the maintenance records. The max. allowable weight (of both floats together) is 7 grams. ATTENTION Replace all floats which exceed the max. weight"

It does.

What I meant was why not do the whole job and then the carbs start from zero when he gets the plane in the air. Cutting corners is ok on your car but aircraft is a bit different.

[facthunter]

"O" rings are not made of rubber.  I said doing it sooner (For an aeroplane ) would be a good idea, because it's IN an aeroplane and how could caution be a bad idea. Nev

[facthunter]

  The LATER floats are mandatory and the check should suffice with those. It's a different material. Plastic float problems are not uncommon with the wrong materials and metal ones have issues as well. Leaks and repaired weights  Nev

[spenaroo]

this is the Yamaha product I mentioned earlier.

works very well, unlike the sprays - not cheap though

 

https://www.citywestyamaha.com.au/product/yamaha-yamalube-carburetor-cleaner-dip-bottle-946ml-motorcycle-maintenence-etc/

Edited September 28, 2023 by spenaroo

[onetrack]

Carburettor O-rings are not natural rubber, as Nev correctly states. They're a synthetic rubber copolymer made from acrylonitrile (ACN) and butadiene, known as Nitrile rubber, NBR, or Buna-N.

Carburettor O-rings can also be made from Viton, which is more durable than Nitrile rubber in high temperature conditions. Nitrile rubber has a maximum operating temperature of 120°C, Viton can cope with up to 210°C.

 

However ... even though O-rings aren't rubber, they degrade from long-term compression (they flatten out), they degrade from UV light and weather exposure, and they degrade over time with regular exposure to high temperatures.

In addition, both Nitrile and Viton can be degraded by acids and chemicals that are not normally found in fuels - but which acids and nitrile-detrimental chemicals can form from interactions between hydrocarbons, moisture and metals, over time.

 

Essentially, an investment in a complete carburettor kit after several years of engine use is a wise investment, especially for an aircraft engine. As I understand it, Dannys engine is a used engine with high hours, and it may or may not have records of when a carburettor kit was last installed. A rough-running engine when airborne, is definitely white-knuckle stuff.

[Blueadventures]

9 minutes ago, onetrack said:

Carburettor O-rings are not natural rubber, as Nev correctly states. They're a synthetic rubber copolymer made from acrylonitrile (ACN) and butadiene, known as Nitrile rubber, NBR, or Buna-N.

Carburettor O-rings can also be made from Viton, which is more durable than Nitrile rubber in high temperature conditions. Nitrile rubber has a maximum operating temperature of 120°C, Viton can cope with up to 210°C.

 

However ... even though O-rings aren't rubber, they degrade from long-term compression (they flatten out), they degrade from UV light and weather exposure, and they degrade over time with regular exposure to high temperatures.

In addition, both Nitrile and Viton can be degraded by acids and chemicals that are not normally found in fuels - but which acids and nitrile-detrimental chemicals can form from interactions between hydrocarbons, moisture and metals, over time.

 

Essentially, an investment in a complete carburettor kit after several years of engine use is a wise investment, especially for an aircraft engine. As I understand it, Dannys engine is a used engine with high hours, and it may or may not have records of when a carburettor kit was last installed. A rough-running engine when airborne, is definitely white-knuckle stuff.

The most usual 'o' ring to break up on removal on the bing is the one for the idle mixture screw, its in the external body so most likely subjected to the most heat.   They can also be damaged when fitting over the hex head as screwdriver slots get a little bit sharpened. Years ago I invested in the rotax tool for fitting this 'o' ring; very useful.  Also a minimal smear of lithium grease assists fitting the 'o' rings.

Edited September 29, 2023 by Blueadventures

[skippydiesel]

1 hour ago, BrendAn said:

What I meant was why not do the whole job and then the carbs start from zero when he gets the plane in the air. Cutting corners is ok on your car but aircraft is a bit different.

My apologies - I thought we/you were talking service interval/content.

Edited September 29, 2023 by skippydiesel

[skippydiesel]

1 hour ago, spenaroo said:

this is the Yamaha product I mentioned earlier.

works very well, unlike the sprays - not cheap though

 

https://www.citywestyamaha.com.au/product/yamaha-yamalube-carburetor-cleaner-dip-bottle-946ml-motorcycle-maintenence-etc/

What concerns me, is the advice, from Rotax Owner Forum, that the carby's have an epoxy sea that may be damaged by a chemical cleaner.

 

I have often been accused and suffered from the application of excess zeal, when it comes to cleaning engine parts - old & doddery now, I hope I have learnt some moderation.

 

The temptation to use  magical bottle/can/packaged repairs/enhancements/cleaners, etc can be very strong - best to resist and do the job the hard way - dismantle & use a tried/recommended solvent,  lint free cloth, soft wood and air to do the cleaning.

[danny_galaga]

Screw it, I think I'll get the full kits. Imagine if my engine started running rough in flight, particularly on takeoff. Theres enough shaking you'd want to shut it down quick smart. 

 

Dlegg, I know where you are coming from. I am involved in the retro gaming scene. With arcade monitors, one of the most common problems is a capacitor going out of spec or failing. Replace that and you are golden..which one though? There's usually dozens. So what people do is use a 'cap kit' and replace every single cap. Problem solved.

 

Two things with that though

1) what a waste.

2) it really is a case of 'they don't make them like they used to'. Almost certainly, all the good caps that just got thrown out, aren't just better quality, but would probably outlast the new one,even though the new one has say a TWENTY TO FORTY YEAR head start 😯

Better to individually test them, and only replace what is broke.

 

I digress. In this case, I think it might be best to just do the whole lot, floats and all. Safety first. And at least I'm not replacing the parts with the equivalent of a Chinese cap kit 😄

Edited September 29, 2023 by danny_galaga

[BrendAn]

1 hour ago, skippydiesel said:

What concerns me, is the advice, from Rotax Owner Forum, that the carby's have an epoxy sea that may be damaged by a chemical cleaner.

 

I have often been accused and suffered from the application of excess zeal, when it comes to cleaning engine parts - old & doddery now, I hope I have learnt some moderation.

 

The temptation to use  magical bottle/can/packaged repairs/enhancements/cleaners, etc can be very strong - best to resist and do the job the hard way - dismantle & use a tried/recommended solvent,  lint free cloth, soft wood and air to do the cleaning.

That would catch me out too. Never seen an epoxy coated carb before. Makes sense though, it would prevent the white powdery corrosion carbs get if they sit  for a while.

[Blueadventures]

1 hour ago, danny_galaga said:

Screw it, I think I'll get the full kits. Imagine if my engine started running rough in flight, particularly on takeoff. Theres enough shaking you'd want to shut it down quick smart. 

 

Dlegg, I know where you are coming from. I am involved in the retro gaming scene. With arcade monitors, one of the most common problems is a capacitor going out of spec or failing. Replace that and you are golden..which one though? There's usually dozens. So what people do is use a 'cap kit' and replace every single cap. Problem solved.

 

Two things with that though

1) what a waste.

2) it really is a case of 'they don't make them like they used to'. Almost certainly, all the good caps that just got thrown out, aren't just better quality, but would probably outlast the new one,even though the new one has say a TWENTY TO FORTY YEAR head start 😯

Better to individually test them, and only replace what is broke.

 

I digress. In this case, I think it might be best to just do the whole lot, floats and all. Safety first. And at least I'm not replacing the parts with the equivalent of a Chinese cap kit 😄

Also consider the cost of the parts and postage and get a quote from Wal to service.  He is reasonable and will do 100%.  the new float brackets need to be set correct; there is a tool for that and worth buying if your doing them up yourself.  Also Wal will check if any corrosion on the float needle seat, if any corrosion there fuel will pour out of the vent hose, very important not to have an issue there.  Sorry if my comments are a pain, but just sharing from my experiences.  Your first flights are to be fun and enjoyable.  Give me a call if you want to know more.  Text first or leave a message and I'll call back if you call.  Cheers.

[danny_galaga]

1 hour ago, BrendAn said:

That would catch me out too. Never seen an epoxy coated carb before. Makes sense though, it would prevent the white powdery corrosion carbs get if they sit  for a while.

It's not the whole carb that is coated. There is a bore that needs to be dead end. So it has a ball bearing sealing it. I think it's pressed in, and then sealed with epoxy.