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)

The important characteristic of floats is buoyancy, not weight. If volume
remains constant, then buoyancy can be determined by measuring weight.
However, reducing volume will also reduce buoyancy. The result could be
increased fuel level, just the opposite of the desired outcome.
The volume of two different brands of floats may not be the same. Therefore
weight alone can not be used to measure buoyancy. The best way to determine
suitability of floats is to install them and measure the height of fuel.
 
I've been flying behind Marvel Schebler floats since the end of October. No fuel smell in the cockpit, finally. I had the good Rotax floats, the better Rotax "replacement floats", the Rotax "replacement floats" for the "replacement floats" and they all ended up sinking. The only difference I could find is a price hike from one part number to the next and longer and less reliability in processing warranty claims.

So glad to have floats that don't overflow the bowl. I wouldn't mess with them.
 
Joe

Imagine a boat floating in water where waterline is 2? below the deck. Now suppose you pump a lot of fuel onboard? the water line raises and the boat is lower in the water. Conversely, if you take weight out of the boat it floats higher and yet the square area displaced remains virtually unchanged.

I think if we take some volume off the top of the float it will float higher in the fuel bowl. Top half of float is above level of fuel if float is doing its job?
 
Jim, Your reasoning is correct. But just because the Marvel Schebler floats are
heavier does not mean that the fuel level is higher. The volume (density) and
shape of the floats must also be considered. Without knowing the fuel level
when using Marvel Schebler floats, why modify them? Maybe the fuel level is
correct as is. Other posters have stated that Marvel Schebler floats work fine.
 
Jim, Your reasoning is correct. But just because the Marvel Schebler floats are
heavier does not mean that the fuel level is higher. The volume (density) and
shape of the floats must also be considered. Without knowing the fuel level
when using Marvel Schebler floats, why modify them? Maybe the fuel level is
correct as is. Other posters have stated that Marvel Schebler floats work fine.


What is of concern is that:

1. There is enough fuel Quantity in the float bowl to prevent fuel starvation at full throttle, with given fuel pressure and fuel flow, under any circumstance.

2. That the float maintains a high enough level of buoyancy to activate the fuel float cutoff valve, so that the fuel level remains below the overflow vent level, and that the cutoff valve functions fully, limiting fuel level in the float bowl when the level reaches the cutoff point.

The relative density of the float material to the relative density of the fuel you are using at the time, controls how high the float sits in the fuel above the surface, with the pin activating the cutoff valve.

I'm sure there is a range of weight that is acceptable to the mass and size of the floats they build, and MS has taken that into account in their engineering of the floats for the Bing carbs, the proper mass and volume of space occupied.

All Rotax and / or Bing carbs has done is determine the amount of weight, for the amount of mass for their floats, that buoyancy is lost in their reference fuel, that it is out of spec, and the floats then need replacement.

It almost sounds like they've gone and measured and engineered a consumable useful life into their carb floats, with a spec in place to replace. Like carb floats are no different that spark plugs, design them so that they become a revenue stream.
 
Jim, Your reasoning is correct. But just because the Marvel Schebler floats are heavier does not mean that the fuel level is higher. The volume (density) and shape of the floats must also be considered. Without knowing the fuel level when using Marvel Schebler floats, why modify them? Maybe the fuel level is correct as is. Other posters have stated that Marvel Schebler floats work fine.

It would be relatively easy to check buoyancy and float actuator pin levels by “floating” a set of <7-gram Bing Vs. stock Marvel Schebler in a bench setup using the Bing float bowl. Simply measure difference of pin height to top lip of float bowl. Perhaps then, the top of the MS could be shaved off to make pin float heights the same. This would be interesting project for sure.

I have emailed Marvel Schebler, Rotax, and Bing to explain the concept of shortened height for Bing 64 floats. Maybe everyone is stuck on the idea that the floats need to be symmetric geometry. By considering asymmetric geometry, and making the floats one-handed, maybe a more permanent solution can found to the dreaded sinking float fiasco…
 
Last edited:
There's something inherently wrong about pulling floats from carbs and doing weight inspections on them, because the fuel you use is damaging them beyond functional use, and creating a fire hazard with leaking fuel.

A closed loop fuel injection system is the permanent solution. Far, far less silly routine maintenance, for those that would rather fly than still wrench on their planes doing inspections or finding hazardous fuel leaks. A float for a carb that absorbs fuel and sinks, failing to work properly is an engineering flaw. Plenty of Carburetor manufacturers for snow mobiles, jet ski's PWC and like type of engines like the Rotax that know how to make and manufacture carb floats that don't fail.
 
Last edited:
See my post #96 above where I explain how we removed the top cowling and ran the electric fuel pump to discover fuel pouring out of the right carb air filter. Luckily, no fire when fuel overflowed the drip pan and sizzled on the hot exhaust stack.

I have been thinking about how to mitigate the possibility of this happening again.

Here’s my plan:

If the decision is to fly the airplane, then upon arrival at the hanger, the first thing I will do is to raise the canopy and turn on master switch in order to power the electric fuel pump. Let the fuel pump run, and if a float is sunk, fuel will overflow the carb and most likely drip on the ground where it can be noticed prior to flight. I plan on letting the electric fuel pump run while I preflight and load the plane.

For what it’s worth…
 
See my post #96 above where I explain how we removed the top cowling and ran the electric fuel pump to discover fuel pouring out of the right carb air filter. Luckily, no fire when fuel overflowed the drip pan and sizzled on the hot exhaust stack.

I have been thinking about how to mitigate the possibility of this happening again.

Here?s my plan:

If the decision is to fly the airplane, then upon arrival at the hanger, the first thing I will do is to raise the canopy and turn on master switch in order to power the electric fuel pump. Let the fuel pump run, and if a float is sunk, fuel will overflow the carb and most likely drip on the ground where it can be noticed prior to flight. I plan on letting the electric fuel pump run while I preflight and load the plane.

For what it?s worth?
Thanks for that tip. Worthy of Checklist/POH IMHO. Just like emergency procedure/immediate action when a carb return spring fails. Worthy!
 
After 53 hours on the 861-184 floats I had to replace them due to fuel leakage. I took the advice of one of the guys who posted "to leave fuel pump on during walkaround" that was good advice, I smelled fuel when I opened the oil service door and heard dripping, sure enough my Left carb was leaking. I called Lockwood and got the latest and greatest a 861-189C and rubber gaskets. The old floats in the LH carb weighed 10g...RH Carb 9g...I guess 10g is the magic number for a leak...new Floats weighed 6g...hopefully these will go more than 53 hours. I used to get a wiff of fuel smell on climb out every now and then just a few hours after the -184 were installed. It was not a constant issue and would clear up after level off. When I would remove the top cowl I never saw evidence of leakage until the other day. Also the engine seems smoother and EGTs better balanced on my test flt...Cost of $352.80
 
Further update to post #96…

I emailed Marvel Schebler and again got no response from them. How can a company in today’s economy have such poor (non-existent) customer relations? Anyway, my friend was able to talk to them via phone and apparently the majority of the original production lot of blue epoxy 912 floats went to Europe and sold out fast. MS says they are working on a sub 7-gram redesign but can’t estimate a time line for delivery.

So, we ordered $150 Bing 861 189 and installed them in the right carb. While we had everything apart, we decided to check the left carb. When we dropped the float bowl, we could immediately saw one of the floats sunk directly to the bottom of the bowl – completely submerged in the fuel. The pair of floats from this carb weighed 10.24 grams. Unbelievable…. Back to the ATM machine and now buying yet another set of Bing floats.

When does this all stop? A single manufacturer for floats that don’t float? The real rub is you have to buy more floats from this same manufacturer that again don’t float. I like that business model – planned failure – and with aircraft safety-of-flight component.

Thanks for listening, I feel better now…
 
Last edited:
Further update to post #96…

I emailed Marvel Schebler and again got no response from them. How can a company in today’s economy have such poor (non-existent) customer relations? Anyway, my friend was able to talk to them via phone and apparently the majority of the original production lot of blue epoxy 912 floats went to Europe and sold out fast. MS says they are working on a sub 7-gram redesign but can’t estimate a time line for delivery.

So, we ordered $150 Bing 861 189 and installed them in the right carb. While we had everything apart, we decided to check the left carb. When we dropped the float bowl, we could immediately saw one of the floats sunk directly to the bottom of the bowl – completely submerged in the fuel. The pair of floats from this carb weighed 10.24 grams. Unbelievable…. Back to the ATM machine and now buying yet another set of Bing floats.

When does this all stop? A single manufacturer for floats that don’t float? The real rub is you have to buy more floats from this same manufacturer that again don’t float. I like that business model – planned failure – and with aircraft safety-of-flight component.

Thanks for listening, I feel better now…

I don't have a dog in this hunt any more but it's hard to conceive that Rotax and/or its resellers aren't taking more ownership / control of this issue. But it's not as bad as the news for V-tail Bonanza owners: there's an active thread on Beechtalk saying that basically the raw materials to make new skins for ruddervators (special thickness/alloy of magnesium) is not available, and Textron isn't motivated to share the data needed for aftermarket suppliers to fill the void. It's being said that once the supply dries up completely (from wrecked / retired airplanes) the ruddervators will represent the entire value of the airplanes. The small volumes of production in any aviation product make the markets kind of crazy.
 
It ends either when they make a float that floats or a reasonably priced throttle body fuel injection system is made for the engine. The cost of these floats is nuts, $75 for each one. I would think a metal or plastic float could be made by Bing to fix this.
 
It ends either when they make a float that floats or a reasonably priced throttle body fuel injection system is made for the engine. The cost of these floats is nuts, $75 for each one. I would think a metal or plastic float could be made by Bing to fix this.

Maybe more a shame someone like MS, Keihin or Mikuni Carburetors can't come up with a workable solution to just replace the Bing CV carbs, altogether.
 
After reading this thread, I'm baffled at how we're 8 years and 450+ hours in on or original floats. Of course having said that, when I start the CI on Monday I'm sure I'll find all four sunk to the bottom of the float bowls.
 
Today I am installing the third set of new floats.........this year.

Dave

Any chance you could send me one or two sets of your old heavy floats. I still want to experiment and see if I can't hollow out the float and leave a large air bubble in the center. Long shot... but it might work.

Send me email and I'll forward my shipping address. I can pay postage easily if you have PayPal.

[email protected]
 
Any chance you could send me one or two sets of your old heavy floats. I still want to experiment and see if I can't hollow out the float and leave a large air bubble in the center. Long shot... but it might work.
I also wonder about the possibility of drying the floats out (ambient air or even a low temp bake, maybe) and coating them with something impermeable to keep them from absorbing gasoline.
 
I also wonder about the possibility of drying the floats out (ambient air or even a low temp bake, maybe) and coating them with something impermeable to keep them from absorbing gasoline.

Exactly. I'm pretty sure the absorbed fuel does eventually "bake" out. I've been thinking about this for a while. Maybe conformal coating used for electronic circuit boards. Don't know if it's impervious to fuel.
 
Dave

Any chance you could send me one or two sets of your old heavy floats. I still want to experiment and see if I can't hollow out the float and leave a large air bubble in the center. Long shot... but it might work.

Send me email and I'll forward my shipping address. I can pay postage easily if you have PayPal.

[email protected]
Says he's sent them in with a warranty claim.
 
Really sad

I'm really disheartened by this development. I have not even fired up my Rotax yet and realize that I will likely be paying Rotax a 'use tax' in order to fly my 12. How much maintenance money must be put away in order to fly Rotax carburetor floats? So, if I burn 5 gallons of fuel an hour how many miles do I get off a set of carburetor floats? Gee manee!!!

This problem hasn't been solved by Rotax or their distributers and it has been a known problem for the 912 engines for quite some time now. I likely will get my 12 flying and then sell it to someone along with the warning that they will likely have to pay Rotax or some other company for replacement floats once in a while. I can't imagine what is holding up a solution to this problem.

If I were a betting person, I'd bet that Rotax has a legal problem with 'fixing' this obvious engineering defect. There is plenty of documentation to open the door to a hugh lawsuit against Rotax and its associates after the unthinkable happens. And I suppose that the FAA will ground all 912 equipped airplanes in the US after someone dies and it can be proven that Rotax engines had a known defect which they refused to attempt to correct.

And, how about those exorbitant prices of new floats? Is the price inflated in order to pay for an already filed or anticipated law suit?

Are pilots/operators of Rotax 912 engines of other countries having this same problem? Has the appropriate US facility been notified? NTSB? EAA? AOPA? other? How about Van's? are you guys and gals filing the appropriate Van's feedback paperwork? I can't believe that Van's doesn't care.

This problem greatly reduces the value of my brand new 912 powered RV-12. I had hoped that this would be my first and last airplane. I really don't want to become a Rotax Float Daddy. I am inclined to think that this problem will or has already killed someone. Sad.

I'm having second thoughts about even attempting to fly my 12 when it is completed and certified this year. I'm pretty well bumbed out - :(::mad:
 
Ed,

You should be able to file a warrantee claim on the defective floats with Rotax should you also have an issue. Just be prepared to wait six to nine months to get your money back. Pretty sad! You will find that they insulate themselves from customer complaints. I have never been able to find names, emails addresses or phone numbers for their executive team. They don’t seem to define “customer service” the same way we do here in the US.

Other than the continuing carburetor float issues and some problems with jittering oil pressure (resolved), the 912ULS has been a great engine. As for someone dying from the sunken floats, I don’t think its likely. While the fuel mixture gets real rich with the saturated floats, the engine keeps running, perhaps a bit rough.

Alex
 
E.D.,

Don't get too wrapped around the axle on this. Like I said, I've got 450-plus hours on the original set of floats. Defective design? Defective material? Just random defective parts off the line? I don't think we really know for sure. Maybe yours will sink, maybe they never will. If you have your engine already, maybe remove the floats from the carbs and let them sit in a jar of gasoline while you build. After a few months, take 'em out and weigh them. It shouldn't matter if they're in the engine or in a jar, absorbing gas is absorbing gas.
 
I did some searching today for coatings that are impervious to gasoline. One company I contacted (Klass Kote Quality Coatings Division, Eagan, Minnesota) replied back as follows:

I asked... Do you have a two-part paint that is 100% impervious to automotive gasoline?

I have a carburetor that has composite floats that absorb gasoline over time. I want to paint the floats with a paint that can stand constant submerging in automotive gasoline.

Reply... Absolutely! - Our 2-part Klass Kote epoxy paint system is completely impervious to gasoline fuel, no problem. We have had quite a few customers use it to paint their carburetor floats. Be sure to completely clean the surfaces of the floats and wipe them down with our epoxy reducer #500 before coating. Then wait at least 7 days at 70 F for full sward hardness cure, before putting the floats back into service.

--------------------

Now I need a set of floats to try this coating. Anybody have an old set of floats for an experiment? Maybe we can solve this problem once and for all...
 
I'll be following your experiment with interest. IMHO, I think that the various additives (ethanol being just one) added to auto fuel by various states may be the cause of the floats' absorption of fuel. I've been using Shell 91 with ethanol (Ugh!) out here in California and the Rotax/Bing floats are not surviving the exposure.

ps -- The weight of the added coating may prove problematic?
 
I am wondering if the "Klass Kote" is the "Glass Kote" referred to in some of the R/C forums that I found when searching this afternoon.

I was wondering about the effectiveness of some of the newer epoxy paints as well. The automotive stuff is pretty robust, but of course none of it is tested for long term exposure to automotive gasoline, with or without ethanol. Cerakote looked like it might be worth testing as well.
 
E.D.,

Don't get too wrapped around the axle on this. Like I said, I've got 450-plus hours on the original set of floats. Defective design? Defective material? Just random defective parts off the line? I don't think we really know for sure. Maybe yours will sink, maybe they never will. If you have your engine already, maybe remove the floats from the carbs and let them sit in a jar of gasoline while you build. After a few months, take 'em out and weigh them. It shouldn't matter if they're in the engine or in a jar, absorbing gas is absorbing gas.

Ditto!! Do new rv12 SLSA?s owners under warranty have to fend for themselves?
 
Floats

How about a thin coat of pro-seal, can it be thinned down to paint thickness to seal the floats.
 
There are lots of good candidates for coatings including thinned two-part epoxies that can be sprayed with an airbrush. Pro-seal would be difficult to work with and probably result a thick/uneven coating.

I'm willing to invest time for this endeavor. I will do the research and leg work but what I need is a good selection of floats for experimental testing.
 
Bing carbs

I have these same floats on a HKS700E flying for the last 2 years. Building a RV-14A and about 50% though this airframe. Engine arrives in a few week. I dropped the bowl on my 2 Bing 64CV carbs on my engine. 3 were at 3.1 grams and the third at 3.38 grams. Will keep an eye on these. Great posts on VAF, thanks for letting me know of the issue. HKS never said a thing.
 
It looks like I?m joining the ?club? myself. I?ve been having rough engine in mid-range and now rough idle after hot restart. 5500 rpm cruise remains very smooth. Yesterday?s flight had a slight fuel vapor smell in initial climb. These floats are original with 425TT using 93E10 exclusively.

I?d like to use Marvel-Schebler floats but they are unavailable. Last we heard they are redesigning to achieve 7-gram weight. So, I placed an order with LEAF for 861-189 floats and new bowl gaskets. $345... :eek:

I?ll install floats later this week and report back on condition/weights of floats as removed. The old floats will be left out to ?dry? and then stowed in the airplane to be used on-the-road if necessary.
 
That was the first sign, smelling gas at climb out, I put about 50 hours on them is all, then got the -189C from Lockwood, we'll see how long these last.
 
It looks like I?m joining the ?club? myself. I?ve been having rough engine in mid-range and now rough idle after hot restart. 5500 rpm cruise remains very smooth. Yesterday?s flight had a slight fuel vapor smell in initial climb. These floats are original with 425TT using 93E10 exclusively.

I?d like to use Marvel-Schebler floats but they are unavailable. Last we heard they are redesigning to achieve 7-gram weight. So, I placed an order with LEAF for 861-189 floats and new bowl gaskets. $345... :eek:

I?ll install floats later this week and report back on condition/weights of floats as removed. The old floats will be left out to ?dry? and then stowed in the airplane to be used on-the-road if necessary.

Why don't you experiment with them with a coat of epoxy, instead, like you said you would with other's floats? Now you have your own pair to experiement with?
 
The Type "A" tank sealant has the consistency of honey. If anyone is trying a Pro-Seal coating, if might be easier to start with that. Skygeek.com sells it.

It's normally used to overcoat the joints and rivet heads in tanks. I used a hobby syringe to apply it.

Dave
 
Yesterday’s flight had a slight fuel vapor smell in initial climb.

Jim - I've had this symptom before this time of year ..... even with new floats. I think some of it could be using winter blended auto fuel when the temperatures are becoming summer like. As an example, last spring I caught a slight whiff of fuel during takeoff on one of the first warm days of spring after being on the ground for quite a while holding for traffic. I went to the hangar and drained out enough fuel to add 100LL to get the mixture around 30% and ran that way until the summer fuel hit the service stations June 1. Never a hint of fuel smell nor all summer long while running the summer blend. Then after the winter blend began September 1 there were a couple of warm days where I was held on the ground longer than usual and once again there was a slight whiff of fuel.

So although the carb floats have been, and apparently continue to be, truly problematic ... one can't overlook the reality that using winter blended auto fuels on warm days is also problematic. Frankly, I for one can't wait until the new crop of unleaded aviation fuels with a consistent RVP (Reid vapor pressure) are available at all airports.

Happy flying,
 
Last edited:
Whiff's

John, this is Doug in IL. Thanks for your build and now opns experiences, neat to follow! In this thread, in addition to gas, the word that comes to mind is also Carbon Monoxide. Assuming the path of that gas 'whiff' you notice from time to time involves the firewall, have you checked in all phases of flight, throughout the seasons, for CO leaks with a sensitive detector?
Thank you!


Jim - I've had this symptom before this time of year ..... even with new floats. I think some of it could be using winter blended auto fuel when the temperatures are becoming summer like. As an example, last spring I caught a slight whiff of fuel during takeoff on one of the first warm days of spring after being on the ground for quite a while holding for traffic. I went to the hangar and drained out enough fuel to add 100LL to get the mixture around 30% and ran that way until the summer fuel hit the service stations June 1. Never a hint of fuel smell nor all summer long while running the summer blend. Then after the winter blend began September 1 there were a couple of warm days where I was held on the ground longer than usual and once again there was a slight whiff of fuel.

So although the carb floats have been, and apparently continue to be, truly problematic ... one can't overlook the reality that using winter blended auto fuels on warm days is also problematic. Frankly, I for one can't wait until the new crop of unleaded aviation fuels with a consistent RVP (Reid vapor pressure) are available at all airports.

Happy flying,
 
Doug -

To answer your question. No ... I have not tested for CO probably not a bad idea to do so.

That said, I have flown very slow steep angles of attack for extended periods of time and have never had the slightest whiff of fuel while in the air. I have never had the slightest whiff of fuel while using a blend of at least 30% 100LL and winter blend auto fuel with ethanol. I have never had the slightest whiff while using summer blend auto fuel.

The ONLY times I have the hint of any fuel smell is during climb-out when there is winter blended auto fuel in the tank ... typically during a really warm day and/or I have been held on the ground for an extended period of time by ATC.

Happy flying,

John
 
Follow-up to post #132 above...

So, I spent $345 plus shipping for two sets of 861-189 floats and two gaskets. I did the installation this morning and took my digital gram scale with me to measure the old floats, and you guessed it, each pair of floats weighed less than 7 grams. Original floats with 428TT and 100% 93E10. Nuts...
 
Repeat

112 hours and I have replaced my floats twice.
I just installed the newest replacement floats that have an R on them.
Has anyone had them fail? Just curious.
 
I experimented with the MS blue floats for almost 35 hours some time ago. Did not see any definitive bad effects but had the perception that the ran a bit rich at low power settings. I have Bing floats in now but if they go bad I'm returning to the MS floats. If I do that I'm thinking that I might remove some material from the top of the floats to reduce their weight without affecting their normal displacement.

The issues we've had over the years with these floats are unacceptable. I've lost count but I think I'm on at least my 4th set of Bing floats in a bit over 4 years. That's a lot of $$$, not even counting the frustration and safety issues, for a product that seems to be just rolling part numbers without any real improvement in performance.
 
The vast majority of my flying has been with ethanol Mogas, don't know about others ...

True, but if running Mogas, your gearbox isn't being exposed to lead in suspension in the motor oil, either, and you can, if you want to, run a full synthetic motor oil like Mobil 1 4T 10w-40 and do 100 hr oil changes. Just a thought....
 
Yeah, I waffled around with oil change intervals for a while but decided that oil is cheap, relatively speaking :), and 50 hr oil change intervals would keep my engine happy. Rotax says 100 hr is OK, just my preference for the 50 hr interval.
 
For what it's worth, two consecutive Blackstone oil analysis reports at 100 hour intervals have shown that the oil and engine are both happy. We run unleaded ethanol-free 91 AKI mogas almost all the time -- on occasional tank of 100LL if we're away from home and have to refuel, but I'd say 90% pump mogas.
 
Back
Top