Cleaning carbies/looking for blockages.. tips?

[danny_galaga]

The following is what I've done. What else should I do? 

 

Finally started my Rotax 912 for the first time last week Ran smoothly for all of 30 seconds. Then really roughly. Then shut it off and called it a day because it was getting late. Had time to think on it, and thought maybe I hadn't tightened up all the cables and doo dads. The throttles are in the swinging arm rests so there's a lot going on (it is what it is, let's not debate what the best design is).

 Anyway, I adjusted everything. Hoping that it was just running unbalanced. Didn't make a difference. Next guess was a blocked jet in a carbie or something. Because I always half arse everything , I found I could loosen the carbies, and remove the bowl without having to undo the cables and hoses.

 

At first glance the bowl looked quite clean, but when I looked closer I could see that petrol 'varnish' that can occur over time. Not heaps, but it could cause a problem I guess. So I carefully scrapped all that off and rinsed with turps. 

 

I also took out the (pilot?) jet. I couldn't tell at first if it was blocked or not. But after a bit of blowing I could see all the way through. Could have been blocked, or just fuel in there blocking the light. I poked a copper wire through to make sure. 

 

The jet in the bowl (choke? Idle?) was clearly fine and I could blow through that. 

 

Once assembled again I still had difficulty starting it. When it did start, it ran smoothly maybe be for a second or so and then roughly again. 

 

I did a few times in case something got sucked through but I'm guessing that wouldn't be likely to happen. Because in total it was enough time for the cylinders to warm a little, I noted that the right cylinders were cooler than left, which seems to me to indicate the problem is the right carbie.

 

Oil pressure was good.

 

Spark plugs looked ok.

[danny_galaga]

So then, I feel I need to take the carbies off completely. If I was smarter I would have cleaned them BEFORE I put the engine in 😄

 

In general, and in particular with Bing carbies, what should I do?

Are there other jets I should give attention to? I have a compressor there, is it safe to give every orifice I see a good enema? I guess there is a diaphragm in the top part, is compressed air likely to damage it?

 

I'm not keen an whacky chemicals etc like carby cleaners. How far do I need to disassemble? 

Edited September 24, 2023 by danny_galaga

[onetrack]

Carby cleaners are a very effective and approved method of carburettor and jet cleaning, far safer than poking around with tools.

 

Carburettors develop deposits as the chemicals in the fuel react with metals and moisture, as the residual fuel evaporates.

[Blueadventures]

Did you do correct mechanical balance, o rings dry out and crack, what floats model there is a bulletin on them. Can sink and flood engine.  I’d get a carb kit through them by an experienced person, not hard but follow the manual.

[IBob]

I would start by checking the idle jet and throttle stop settings, as per the Rotax manual. This is a quick static setup and should be checked anyway. Setting at the factory can be a bit rough.

 

You mention having trouble starting: are you starting using the choke? This requires the throttles to be entirely closed, or the choke will not work.
I normally start a cold engine, even on mild days, using the choke, then transition to the throttle. The choke has it's own jet etc, almost like a mini carb within the carb, I would get that going first.

 

Maybe also check that your floats are okay, this is done by weighing them.

[Blueadventures]

Being new build, engine with hours on it and been sitting. Best to do carb clean, service and mechanical balance as per manual. You don’t want surprises or extra distractions during first and during the next 25 hours.

[Kiwi]

Did you purge the oil system? A rough running Rotax can be more than fuel and spark.

 

 

 

[danny_galaga]

Engine purged. First start it ran about as smoothly as the last time, which was earlier this year from memory. Since it actually ran well the first time it started last week, I feel some things can be put down the list. 

Since it ran well on the first start, I feel I don't have to worry about the floats or oil purge as possible causes of the following rough running 30 seconds or so later. Seems most likely to be a carby issue, as in some kind of blockage. Ibob, I will pay particular attention to the chokes. Just looking at them from the outside I can see they are quite an elaborate lil beastie!

If carby cleaner is used, is there any brand I should use, or avoid? 

 

I also have maybe 20 hours flying behind this engine, and it was very reliable. I know that doesn't preclude other problems happening. Just a FYI. It was running well when removed from the aircraft, and has about 1800 hours on it. Regularly serviced.

Edited September 24, 2023 by danny_galaga

[Blueadventures]

I had an engine (R912UL 80hp) sit while repairing undercarriage.  Then ran rough.  6 weekends of trouble shooting; new o rings, checking for air leaks etc.  Eventually found a build up of crap up around the mixer tube; looked like an o ring.  Then ran absolutely great.  There are many reasons for rough running.  another is your carb bowl vent lines and how they are set (you don't want to extend into slip stream as will pull fuel.  You must take the time and verify the floats are correct and not heavy.  Enjoy the build and carb sorting; look forward to hearing about first fly.

Edited September 24, 2023 by Blueadventures

[Kiwi]

To add to the confusion with the chokes, the left side has a "R" on it and the right side has a "L" on it.

[dlegg]

The fact that it starts and runs fine for 30 secs, I would be looking at the fuel delivery system. Next time run it, when it runs rough shut it down and remove the float bowls and see what fuel level is in there. Good starting point for diagnosis.

[facthunter]

Kiwi, that's probably a relic of them being from a BMW motorcycle. I'm not a great fan, but if you or anyone is not familiar with this kind of stuff find someone who is.  The FAA even said when the dashpot stuck open the motor flooded which IF you know anything about CV Carburettors,  is Bu!!$#!T. I  emailed them and didn't get a response. . However it's on a plane motor now so treat it accordingly.  Nev

[Kiwi]

At least it's correct on a pusher aircraft. 

[danny_galaga]

16 hours ago, dlegg said:

The fact that it starts and runs fine for 30 secs, I would be looking at the fuel delivery system. Next time run it, when it runs rough shut it down and remove the float bowls and see what fuel level is in there. Good starting point for diagnosis.

I should emphasise, it ran well on the first start, then after 30 or so seconds, roughly. Since then it has not run smoothly. Feels like a carbie issue. Not sure how much fuel will stay in the bowls if I remove the carbies. There's no way of removing them without swivelling the carbies...

[Blueadventures]

47 minutes ago, danny_galaga said:

I should emphasise, it ran well on the first start, then after 30 or so seconds, roughly. Since then it has not run smoothly. Feels like a carbie issue. Not sure how much fuel will stay in the bowls if I remove the carbies. There's no way of removing them without swivelling the carbies...

Were you still at low rpm, say about 2000 to 2200 rpm or had you increased the rpm a bit at the 30 sec time.

[spenaroo]

Yamaha used to do a carby cleaning product that was the sh%T.
just fill an ice cream container and drop the carbies in overnight, loved by bike mechanics everywhere.

 

these days we used ultrasonic cleaners:

https://www.ebay.com.au/itm/295183469452?chn=ps&_ul=AU&_trkparms=ispr%3D1&amdata=enc%3A1hVujQU3FQDy6fJ9MzxSIzg46&norover=1&mkevt=1&mkrid=705-139619-5960-0&mkcid=2&mkscid=101&itemid=295183469452&targetid=1598469861838&device=c&mktype=pla&googleloc=9070901&poi=&campaignid=19657035767&mkgroupid=143201283022&rlsatarget=aud-1175687084793:pla-1598469861838&abcId=9305369&merchantid=7364522&gclid=Cj0KCQjwvL-oBhCxARIsAHkOiu2kAeputT-OjtX-PVg7yFY88_2Z4xbdTeOC-QDxktyh-3KHqqd_3aYaAm4VEALw_wcB

might have to run it through a few times. especially if running mogas, it isn't what it used to be.

we noticed the fuel doesnt go off so much as turn to jelly now.

[skippydiesel]

Rotax specifically warn against using ultrasonic cleaners on the carburettors;

 

From Rotax Owners Forum:

 

https://www.rotax-owner.com/en/912-914-technical-questions/10074-why-is-there-glue-on-my-caburetors

[BrendAn]

how old are the needles. a lame showed me the worn needles he changed out on his own 912 when it started running rough . your carbs might be due for a full rebuild.  how old is the fuel in your lines and filter , might be a bit off if it has been sitting a while.

[BrendAn]

    part number 16

[danny_galaga]

New build airplane  I only put fuel in it when I was ready to start it a couple of weeks ago.

 

Engine is I think 2017, 1800 odd hours on it. As far as I know they are the carbies that were on it when it last ran but admit I can't be 100% sure.

 

I will take the carbies off this weekend and take them home to work on them in a (relatively 😄) clean environment. 

 

I guess strip the major components, soak in carbie cleaner? Inspect for wear/damage of needles/O rings / gaskets etc? 

 

I'll have to find my beam balance weights I made years ago to weigh the floats..from memory they went to 0.1 grams. I'm guessing that will be accurate enough 😄

Edited September 26, 2023 by danny_galaga

[facthunter]

Use lint free cloth if you use it at all.. Check you floats are the correct ones. Blow out with compressed air. Lay it all out on a clean sheet so you don't lose small items. Align the little tit in the diaphragm properly. exercise it before tightening.   Nev

[pmccarthy]

Double check floats.

[Blueadventures]

7 hours ago, danny_galaga said:

New build airplane  I only put fuel in it when I was ready to start it a couple of weeks ago.

 

Engine is I think 2017, 1800 odd hours on it. As far as I know they are the carbies that were on it when it last ran but admit I can't be 100% sure.

 

I will take the carbies off this weekend and take them home to work on them in a (relatively 😄) clean environment. 

 

I guess strip the major components, soak in carbie cleaner? Inspect for wear/damage of needles/O rings / gaskets etc? 

 

I'll have to find my beam balance weights I made years ago to weigh the floats..from memory they went to 0.1 grams. I'm guessing that will be accurate enough 😄

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.

[danny_galaga]

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

[Blueadventures]

44 minutes ago, danny_galaga said:

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

Part of the 5 year rubber.  I only mentioned above because I have serviced and chased issues with a number of carbs and find long time in service 'o' rings are at times hard, worn and break into pieces when the part they are on is removed.  So if you don't have new ones on hand you need to order and await delivery. I keep some parts on hand as I assist owners at times.  Cheers Mike.

Edited September 26, 2023 by Blueadventures