What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

New member of the 'Sinker Club' (carb floats)

Maybe being just a little past the acceptable level would explain the intermittent nature of the problem.

Any progress to report?

I think setting float level on low end of spec is a good experiment. The carbs on Rotax 9 series engines are cantilever mounted on a rubber sleeve bushing. What makes matters worse is the heavy air filter at the un-supported end. A mickey-mouse extension spring attached to the top of carb is used to counter the overhung weight.

I think the fuel inside the float bowl is very un-settled on an aircraft engine and especially so on the Rotax 912. Turbulence can throw the fuel in every direction making float level control challenging. At cruise power setting float level is not so critical because fuel flow is much higher. Engine runs smoother at cruise speeds as well and carbs don?t dance around so much.

Every 912 I have seen does a dance at lower engine speeds. Imagine how floats are trying to set correct level when carbs are jumping around. So, if floats are wiggling around and level is trending high, this is condition for rich mixture and/or float bowl overflow. The condition is worsened because fuel flow for combustion is low at slower engine speeds.
 
A mickey-mouse extension spring attached to the top of carb is used to counter the overhung weight.

The spring was added to the engine design early on, not to support the filter weight, but to change the natural resonant frequency of the carb / engine interaction which caused a failure of the carb. mounts.
A different / more durable carb mount was introduced later but they left the spring.
 
so here is the update

After doing all of following.

1.comlpete carb overhaul both sides both and both fuel pumps new

2. complete removal of coils testing with ohm meter both hot and cold and test all pick up coils the same way
(when doing this i found one of the coils was rubbing/chaffing bad on the motormount .it actually wore through the powdercoat down to the metal motor mount is OK)

I thought oh boy I found the problem. No to be.Same issue returned.

Here is the interesting part. With the top cowl off and cool air flowing over the top of engine and not retaining heat I could not re create the problem.

Put the cowl back on and problem returned.for sure heat related.

I ask myself the question what else is on top of the engine that heat is getting to. THE FUEL SYSTEM. I am thinking vapor lock ??.

Sure enough drained all the fuel and put in new 93e10. problem solved

3 weeks of trouble shooting and all is well.
Now why wouldnt I check that first you ask. Well I have had 93 no ethanol premium deliver to the farm here for 10 years and always added stabil to all the 300 gal delivery. Never had a problem in 10 years and 1000 hours.

I always thought thats why my 1000 hour floats are still good less that 6g

All the things I replaced that I mentioned above needed to be done anyway due to 1000 hours so not all wasted.

The only thing I dont like is running 93e10. (CarbFloats)I will have to find another supplier for premium 93 with no ethanol. I think last delivery was bad stuff.

Thanks for all your replys

Brad Stiefvater
 
Interesting. Auto fuel does not store well even with stabilizer added. Octane rating takes a hit. Running fresh 93E10 is Rotax recommendation.

I wouldn't worry about floats - its pretty much out of our control. Take a spare set of carb floats and tools in the airplane for emergency change-out.

Thanks for report - glad things worked out.

Stay safe...
 
Well I have had 93 no ethanol premium deliver to the farm here for 10 years and always added stabil to all the 300 gal delivery. Never had a problem in 10 years and 1000 hours.

Brad,

Your experience sounds to me as though it may very well have been a heat related vapor lock issue. In our area, the summer blend fuel has a mandated RVP (Reid Vapor Pressure) not to exceed 9 psi between June 1 and September 15 ... the winter blend has a much higher RVP meaning it evaporates much easier. (Also of note ... the winter blend RVP can fluctuate wildly depending on the local temperatures at the time it is refined).

So I'm wondering ... is the 93 non-ethanol fuel you purchase for your farm subject to the EPA's winter/summer blend mandates? If so, you may may have been typically purchasing fuels during the summer period and hence having no issues with running it in your Rotax engine ... however, your last purchase may have been a winter blend, which would certainly explain the issue you were experiencing now that the outside temperatures are becoming more summer like.

Anyway, glad to hear changing fuel solved your issue.

Happy flying,
 
Dec-2020 / Rotax Mandatory (Float) SB

Here it is ladies and gentlemen... the latest addition to your Rotax/Bing float collection! But wait, there's more; Rumor has it that work has begun on a custom shadow frame so you proudly display your float collection. Details to follow.

LINK to Rotax UL SB >> https://legacy.rotaxowner.com/si_tb_info/serviceb/sb-912-074ul.pdf

============================================================

SNIPIT

Rotax%20UL%20SB%20%28Float%29%20SB-912-074UL-L.jpg
 
Last edited:
Yes found it in the meantime.

It is getting riduculous. They make more money on floats then engines.
If you read SB 74UL an 74 you are all confused. Its a puzzle.

The engine serial number is clear and after its a lot of if then else

I think easiest is to directly pull the bowls and check for the R and replace if no R

This will be float type number 5 or 6 ?

The engine is running fine for two years after the third replacement. Pffffff
 
The new (newest) Marvel Schebler epoxy floats, reported to weigh 2.9 grams, might be the way to go...
 
I replaced mine with the Marvel Schebler floats last week.

3 weighed 2.8
1 was 2.9

I'll check them every 3 months to see if they are gaining weight.

BTW...The floats I replaced weighed 7.1 total on the right carb and 8.3 on the left. My last condition inspection was done in April and they were at 6.2 and 6.3.

I've replaced the floats 3 times, 12 floats in 6 years. Hope the ones from Marvel solve the issue.

Gary
 
Yes found it in the meantime.

It is getting riduculous. They make more money on floats then engines.
If you read SB 74UL an 74 you are all confused. Its a puzzle.

This will be float type number 5 or 6 ?

Apologize for linking to the Certified SB in my original post... all fixed now.

I too have lost track on the number of Rotax/Bing float revisions. The list below was taken from the Certified SB. Staggering!!

Rotax%20Float%20SB%20x-L.jpg
 
I just had a thought…. maybe if the Marvel Schebler epoxy floats actually “float”, and permanently solve this problem, then there could potentially be several thousand Rotax/Bing floats that could be re-purposed for a better cause. This could be a fitting tribute to the 217 posts in the New Member of the 'Sinker Club'

  • Because the “floats” actually “sink” how about we donate them to make an artificial reef to help save marine life? An ecological project to offset burning fossil fuel.
  • Or, donate thousands of the geometrically-identical floats to the EAA Museum and commission an artist to make a Rotax/Bing display.
  • Or, EAA could use them to make a pathway in one of the lower-laying areas (read swamp) during AirVenture.

Maybe to be equitable, the guy who spent the most money on floats should get an extra vote.

I do my best thinking on Saturday mornings.

Suggestions welcome…
 
Last edited:
Frankly, I’m fed up with the Bovine Sludge from Rotax regarding their carburetor floats. It really rubs me the wrong way that us Rotax owners are continually paying full price for the latest “new and improved” carburetor floats to the tune of $300 (for both carbs) in the "hopes" Rotax finally got the float design/manufacturing right this time. It's as though we are continually paying for Rotax’s research and development efforts to fix their seriously flawed design/manufacturing issues.

I’m not an engineer, so perhaps someone more knowledgeable can chime in … but to me, the heart of the problem appears to be the flawed concept of attempting to thinly seal a micro bubble porous foam material using resins as opposed to just molding the floats as a solid single piece … much the same as the epoxy floats Marvel Schebler has manufactured for the Rotax 912.

I can’t speak for others, but I’m NOT purchasing another two sets of Rotax carburetor floats without first giving the Marvel Schebler floats a try. To me they appear to be designed correctly ... solid, as opposed to a thinly sealed porous micro bubble foam material that, as we all know all to well, doesn’t stay sealed over time.
 
Last edited:
Frankly, I’m fed up with the Bovine Sludge from Rotax regarding their carburetor floats. It really rubs me the wrong way that us Rotax owners are continually paying full price for the latest “new and improved” carburetor floats to the tune of $300 (for both carbs) in the "hopes" Rotax finally got the float design/manufacturing right this time. It's as though we are continually paying for Rotax’s research and development efforts to fix their seriously flawed design/manufacturing issues.

I’m not an engineer, so perhaps someone more knowledgeable can chime in … but to me, the heart of the problem appears to be the flawed concept of attempting to thinly seal a micro bubble porous foam material using resins as opposed to just molding the floats as a solid single piece … much the same as the epoxy floats Marvel Schebler has manufactured for the Rotax 912.

I can’t speak for others, but I’m NOT purchasing another two sets of Rotax carburetor floats without first giving the Marvel Schebler floats a try. To me they appear to be designed correctly ... solid, as opposed to a thinly sealed porous micro bubble foam material that, as we all know all to well, doesn’t stay sealed over time.

It's a BING carburetor problem, Rotax just subcontracts to Bing Carburetors to get new floats. Send your complaints to Bing, just as you would Quadrajets, or Holley or Rochester carburetors on your V8, or Mikuni or Kehin on your japanese motorcycles.

The folks that own the S-LSA versions of the RV-12 are the ones in a bind, they can't use the MS floats.
 
I’m not an engineer, so perhaps someone more knowledgeable can chime in … but to me, the heart of the problem appears to be the flawed concept of attempting to thinly seal a micro bubble porous foam material using resins as opposed to just molding the floats as a solid single piece … much the same as the epoxy floats Marvel Schebler has manufactured for the Rotax 912.

My guess is the juncture where the body of the float is molded around the brass slider tube is where the fuel begins to penetrate the underlying foam.
 
I'm a new Member of the sinker club

Welp - I'm a new member. I went to the hangar to start the install of my Reiff Engine Pre-heater and figured I might as well check the carb floats given this thread and the latest SB since I had the cowl off.

Needless to say I'm a new member of the sinker club. UGH! My weights:

Left Carb

Float 1: 3.58g
Float 2: 6.68g -> WOW

Total: 10.26g --> Out of spec

Right Carb
Float 1: 3.72g
Float 2: 4.33g

Total: 8.05g --> Out of spec


So, I just bit the bullet and spent $369.90 for the Marvel Schebler floats. That's crazy expensive for what they are. But, if it's permanent, I figured no reason to skimp. We'll see. When the come in, I'll also weight them before I install and report back.

QUESITON: Should I also order new gaskets or leave the ones in place that are there?

Fuel used almost exclusively Costco Premium 93 octane.
 
Last edited:
It's a BING carburetor problem, Rotax just subcontracts to Bing Carburetors to get new floats. Send your complaints to Bing

Niner- I'll concede Rotax likely does not directly manufacture the floats ... but I believe reading somewhere, quite a while ago, they were involved with changing the manufacturer of the floats and the testing process.

The latest float part number change will be the fourth since I have owned my Rotax engine (received in 2015) ... I don't know off hand how many changes were made prior to 2015. Be that as it may, it still gulls me to no end that Rotax is charging us owners full price for replacement floats. No exchange program, no cost + handling offering, or at the very least any type of modest discount for those of us that have previously changed the floats to comply with previous service bulletins. Yet, obviously, Rotax KNOWS the floats they've been supplying us have deficiencies or they would not have instituted yet another version of the floats accompanied by a mandatory service bulletin calling for replacement of those floats.

End of rant .... I see Marvel Schebler floats on the horizon, which hopefully will put an end to this nonsense.
 
JFCRV12 --
If you have the thin OEM cork float bowl gaskets I suggest that you throw them out and not reuse them -- IMHO they are whimpy and somewhat difficult to install. I have had consistent success with the slightly thicker green/white composite gaskets as sold by Lockwood/CPS/etc. Do not use any type of sealant when installing these gaskets -- I typically smear a very light coat of white lithium grease on them to help hold them in position during their installation. I reuse them if they continue to look in good condition.
 
Thank you sir. I’ll do exactly that.

EDIT: Do you have a link to gasket or part # by chance? I see them at CPS but out of stock and no delivery until 12/21.

JFCRV12 --
If you have the thin OEM cork float bowl gaskets I suggest that you throw them out and not reuse them -- IMHO they are whimpy and somewhat difficult to install. I have had consistent success with the slightly thicker green/white composite gaskets as sold by Lockwood/CPS/etc. Do not use any type of sealant when installing these gaskets -- I typically smear a very light coat of white lithium grease on them to help hold them in position during their installation. I reuse them if they continue to look in good condition.
 
Last edited:
I found discussion about these bowl gaskets on a BMW forum. The same carb is used on some BMW motorcycles. They have their bowl's off as much as we do and the gaskets have been a problem leaking for them. They found this solution and it has worked extremely good for them. I have them on my carbs with absolutely zero leaks. I

They are made of Viton not cork or compressed cardboard. I don't expect I will ever need to replace them again.

For (2) gaskets they cost me $9.95 plus $6.95 shipping.
Compare to $15.78 for one without shipping at Lockwood.

Real Gaskets Tennessee
Bing 64 carb float bowl gasket
https://realgaskets.com/product/bing-bowl-and-float-bowl-gaskets-bail-type/
 
NOW we're talking :) Ordered.
I found discussion about these bowl gaskets on a BMW forum. The same carb is used on some BMW motorcycles. They have their bowl's off as much as we do and the gaskets have been a problem leaking for them. They found this solution and it has worked extremely good for them. I have them on my carbs with absolutely zero leaks. I

They are made of Viton not cork or compressed cardboard. I don't expect I will ever need to replace them again.

For (2) gaskets they cost me $9.95 plus $6.95 shipping.
Compare to $15.78 for one without shipping at Lockwood.

Real Gaskets Tennessee
Bing 64 carb float bowl gasket
https://realgaskets.com/product/bing-bowl-and-float-bowl-gaskets-bail-type/
 
I found discussion about these bowl gaskets on a BMW forum. The same carb is used on some BMW motorcycles. They have their bowl's off as much as we do and the gaskets have been a problem leaking for them. They found this solution and it has worked extremely good for them. I have them on my carbs with absolutely zero leaks. I

They are made of Viton not cork or compressed cardboard. I don't expect I will ever need to replace them again.

For (2) gaskets they cost me $9.95 plus $6.95 shipping.
Compare to $15.78 for one without shipping at Lockwood.

Real Gaskets Tennessee
Bing 64 carb float bowl gasket
https://realgaskets.com/product/bing-bowl-and-float-bowl-gaskets-bail-type/

For $17.00, this is just cheap insurance to have as spare parts, just in case you need to drop the float bowls to weight the floats and R&R them. Use some white grease, if need be, to hold them in place while reinstalling.

I just ordered a set, too, to have on hand. My floats are holding up well, so far, but there's no guarantee they will forever. Viton is superior o-ring material.
 
Last edited:
I just got off the phone with a gentleman named Mark at Marvel Schebler as I had some questions about their Rotax floats, part number MS80-430. The original Rotax/Bing replacement floats they made were the exact shape and size of the Rotax/Bing float and they were heavier then the 7 gram/pair limit and people didn't want them. He told me they were heavier because they are made from a different material. They have since redesigned the float and it has a different shape and they now come in well under the 7 grams per pair limit.

What may be confusing to some is they still have the old style float picture on their website but if you click the link at the bottom of the page for the "installation instructions" you will see pictures of the new style and shape of the floats that weigh much less than 7 grams.

https://msacarbs.com/product/rotax-bing-blue-epoxy-float-ms80-430/

You can order them direct from MS or any of their distributors. I'm ordering a set today to replace my current 861188 floats that are just a few years old. This will be my 4th set in 7 years.
 
Did you happen to talk about Ethanol absorbtion? I found some posts on the Kitfox or CTFliers forum (I think) where they found the MS floats were absorbing some mogas+ethanol and therefore getting a bit heavier vs. the rotax 861189 floats. Net, now I'm conflicted. I currently have both ordered. Just not sure which way to go.


I just got off the phone with a gentleman named Mark at Marvel Schebler as I had some questions about their Rotax floats, part number MS80-430. The original Rotax/Bing replacement floats they made were the exact shape and size of the Rotax/Bing float and they were heavier then the 7 gram/pair limit and people didn't want them. He told me they were heavier because they are made from a different material. They have since redesigned the float and it has a different shape and they now come in well under the 7 grams per pair limit.

What may be confusing to some is they still have the old style float picture on their website but if you click the link at the bottom of the page for the "installation instructions" you will see pictures of the new style and shape of the floats that weigh much less than 7 grams.

https://msacarbs.com/product/rotax-bing-blue-epoxy-float-ms80-430/

You can order them direct from MS or any of their distributors. I'm ordering a set today to replace my current 861188 floats that are just a few years old. This will be my 4th set in 7 years.
 
You can also buy just the alcohol resistant floats directly from Bing carburetors USA here. These are CV 40mm carbs that you need parts for. Call and ask to make sure they have the RED "R" on them, indicating Resistant.

http://bingcarburetor.com/cv-motorcycle.html

Currently $55.80 each, you'd need 4 of them.

I'm looking for someone's old set of overweight floats to experiment on. Let me know if you have a set, via a PM.
 
Last edited:
Did you happen to talk about Ethanol absorbtion? I found some posts on the Kitfox or CTFliers forum (I think) where they found the MS floats were absorbing some mogas+ethanol and therefore getting a bit heavier vs. the rotax 861189 floats. Net, now I'm conflicted. I currently have both ordered. Just not sure which way to go.

Yes, I did ask him about ethanol in MOGAS because I run MOGAS only but I can get ethanol free MOGAS at an airport about a 10 minute flight from my home airport. He tells me that the floats have been tested with every type of fuel you can imagine with no negative effects. This was a tech and not a salesman. Is it true? I have no hard evidence it is but they must know that Rotax users use fuel with ethanol in it.

If anyone has questions or is unsure I urge you to contact Marvel Schebler yourself and ask them. Their number is 855-672-2272 and they are located in North Carolina.
 
Would you trust either Rotax or Bing after all these years of selling us floats and giving us lousy product? Even the motorcycle guys are fed up. Now “alcohol-resistant” floats with a big RED "R"?

That’s like a wristwatch that is water-resistant – says so on the back of the watch. Resistant is like "oops... a few drops of water got on my watch" and I’d better wipe it off quick. Ever go swimming with a water-resistant watch?

I should have taken a picture of the fuel pouring out of the right side carb air filter a year ago, but instead, I was in full panic trying to prevent a fire…
 
Last edited:
Would you trust either Rotax or Bing after all these years of selling us floats and giving us lousy product? Even the motorcycle guys are fed up. Now “alcohol-resistant” floats with a big RED "R"?

That’s like a wristwatch that is water-resistant – says so on the back of the watch. Resistant is like "oops... a few drops of water got on my watch" and I’d better wipe it off quick. Ever go swimming with a water-resistant watch?

I should have taken a picture of the fuel pouring out of the right side carb air filter a year ago, but instead, I was in full panic trying to prevent a fire…

I have a 2012 RV-12... 2nd hand, owner probably bought the engine in 2011. 240+ hours, Hobbs. Owner kept the tank with 90 octane regular, ethanol free, supposedly, at 4 gallons to 1 gallon of 100LL, to make 92 octane fuel, mixed on a 130 gallon fuel trailer. 8 years on the same floats, so far. I've not been measuring any ethanol, except for the last 23 gallon batch I bought, which was purchased 12-1, and it tests out at about 2.5 to 3% ethanol blend. I may start putting 10% 100LL in the mix, with Decalin for the floats preservation. At least, for now, it's not 10% ethanol.

Fingers crossed, that my floats don't get pickled and sink with some 100LL blended in there. Usually go through 4 to 15 gallons of fuel in a week, so far. But rainy season hasn't quite started here yet... maybe another 3 or 4 more weeks before it starts really dumping rain, and I worry about mogas going sour.
 
Last edited:
I have a 2012 RV-12... 2nd hand, owner probably bought the engine in 2011. 240+ hours, Hobbs.
I think the really old floats may be (holding my fingers crossed here) more or less OK for longer periods. Mine was completed in 2011, don't know when the engine was purchased. We're at roughly 600 hours on the original floats, or at least the same ones that it had when I bought it with 160 hours. We've had a few instances of apparent overflow from the float bowls, but so far it's been gaskets not seated right or the carb not perfectly level. I may need to re-check and adjust the float level. But... you can be sure that if the day comes when we do need to replace the floats, they won't come from Bing or Rotax. If I'm going to toss money into the wind and hope for the best, I'll try M-S first since they don't have quite the extensive track record of producing defective floats.
 
Weighed them with video

https://1drv.ms/v/s!Atwwakv8E39y1I4FXdwfiOSVU96LtQ?e=JTd2Eb

Did the carb float replacement today. Weighed both the Marvel Schebler and he new Rotax floats before installing the Marvel Schebler carbs with gaskets from Real Gasket. Video shows the weighing.

Marvel Schebler came in at about 2.83 ish grams for 3 of them. The fourth was about 2.9 ish. The new Rotax/Bing ones were all about 3.15g.

Anyway, airplane ran great after replacement. Flew for about 15-20 min. No leaks and smooth. Next steps are to check carb sync then prop balance.
 
Last edited:
Did the carb float replacement today. Weighed both the Marvel Schebler and he new Rotax floats before installing the Marvel Schebler carbs with gaskets from Real Gasket. Video shows the weighing.

Marvel Schebler came in at about 2.83 ish grams for 3 of them. The fourth was about 2.9 ish. The new Rotax/Bing ones were all about 3.15g.

Anyway, airplane ran great after replacement. Flew for about 15-20 min. No leaks and smooth. Next steps are to check carb sync then prop balance.

Great info, thanks for sharing. It's nice to see what the actual MS floats look like. Please keep us posted on the performance of the MS floats, it would be so nice to have a final solution! Paul
 
This is an interesting article on float failures in Bing Carburetors. If you read all of it, the author, after soaking floats for years in various brands of gasoline, types of alcohol, and sneaky cosolvents that refiners dump into their gas as "filler" to save on disposal costs of the cosolvents from the refining process, might help shed some light on the failure.

He believes it's the cosolvents that's causing the problems with heavy floats.

He also soaked the floats in 100LL fuel, with no ill effects.

An interesting read, to be sure.

https://bmwmotorcycletech.info/bing-floats.htm
 
Will do. Assuming no obvious issues, I'll keep these in till next CI and re-weigh them then. That's not until next October though. So it will be awhile. And of course, if I do have issues, I'll weigh em and put the new Rotax ones in and see how they go.

Great info, thanks for sharing. It's nice to see what the actual MS floats look like. Please keep us posted on the performance of the MS floats, it would be so nice to have a final solution! Paul
 
Is there any change in the float height setting with the MS floats? Is it the same measurement from the bottom of the float while inverting the carb?
 
Agreed. Rip off for sure. But if they’re permanent and don’t sink I guess it’s worth it
 
Last edited:
Jim,
I wasn’t happy about the processing fee or shipping charge at all but pulled the trigger anyway. After going through 12 floats and being grounded I was desperate. Only time will tell if the MS floats are any better. With no other options at this point we don’t have a lot of choices. Paying the crazy processing fee and shipping charge was easier to swallow than purchasing another 4 Rotax floats. I just don’t trust them.

Gary
 
I asked Marvel-Schebler about the excessive shipping and handling charges for 4 floats that weigh less than 1/4 pound, their answer;

"Thank you for your continued interest.
Unfortunately the shipping costs are calculated by the shipping provider and not by MSA."

It is illegal to "pad" shipping charges, maybe they use an secondary shipper.

ANYWAY, there is a solution, McFarlane sells the same MS80-430 floats for $140.25 per pair and UPS shipping is $20. Roughly a $70.00 savings for 2 sets.
 
I asked Marvel-Schebler about the excessive shipping and handling charges for 4 floats that weigh less than 1/4 pound, their answer;

"Thank you for your continued interest.
Unfortunately the shipping costs are calculated by the shipping provider and not by MSA."

It is illegal to "pad" shipping charges, maybe they use an secondary shipper.

ANYWAY, there is a solution, McFarlane sells the same MS80-430 floats for $140.25 per pair and UPS shipping is $20. Roughly a $70.00 savings for 2 sets.

Surprised you can't specify USPS Priority Mail for shipping method, like at Aircraft Spruce.
 
Back
Top