A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
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Time Online: 36 days 13 hours 14 minutes
I need help solving the problem of an overflowing carburetor float bowl.
It is a Bing 54 carburetor mounted on a Rotax 503 engine. The problem occurred after replacing two sunk floats and installing a carburetor rebuild kit in one of the two carburetors.
The float bowl overflows only after reaching 4000 RPM, the engine can run all day at a lower RPM without overflowing. No matter how I adjust the float level by bending the tab (in a direction away from the floats) that operates the metering valve, the carburetor float bowl overflows. It is possible to adjust the tab so much in that direction that the engine would be starved of fuel/oil. There seems to be no happy median ground.
Fuel gravity feeds from two AirBike wing tanks through a filter and into a dual action pump. I followed the instructions for float adjustments as defined in the Rotax engine manual. The only aberration is that the float bowl fuel level is 1/4" below the bowl rim instead of 1/2" (as it should be) but that is the same level it is on the other carburetor bowl and it doesn't overflow.
When bench examining the carburetor for the "smoking gun," I found nothing out of order except for some corrosion (?) on the seat area where the shut off metering valve's rubber tip makes contact. I polished that area with a hand made tool. A dowel with a piece of cork glued to its end. That was rubbed in a stick of polishing compound. The dowel was chucked into a drill and the bottom of the seat was polished. All debris were flushed out of the carburetor.
With the carburetor inverted on the bench, I adjusted the tab until both float contact arms were parallel with the carburetor housing by virtue of their own weight per Rotax manual instructions. I then reinstalled the carburetor on the engine. No change in performance, the float bowl still overflowed at about 4000 RPM.
When swapping float arm and shut-off valve with the other carburetor, the problem got worse yet the problem did not occur in the non-problem carburetor. I put those components back to their original carburetors. That makes me think it is not a float and shut off valve problem.
Why would the floats allow overflowing only at 4000 RPM or above, why not below that RPM? Perhaps the problem is not in the float and shut off valve but somewhere else? Any suggestions?
I have been trying to resolve this problem for over four months, I hate being grounded. Your comments would be appreciated. Until then, the Huns are having a field day!
Home phone 602-999-3715/Mini-max with Hirth 2704 Ace
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Paul, Seems to me that the problem is that the rubber tip on the float needle is not shutting off the fuel. Since you swapped the needle from the good carb and still had the overflow I would guess that the problem is not with the needle but with the seat on the bad carb. I can't remember if the seat is replaceable or not but if it is that would be my next step. Dick
4000rpm plus? Could it be a strange vibration problem? Swap the carbs front to back and see if the problem moves with the carb or not.
Were you getting overflow with the sunken floats before you noticed they were over-sunk and changed them?
I had fuel on the windscreen from the 503 single carb's overflow on my ferry flight. Intermittently thereafter. Yes, it did turn out to be lazy floats, but the carb functioned on most flights without overflowing, prior to finally replacing them.
Paul I too think the problem is the needle seat. As you said it had some corrosion but you cleaned it with a flat dowel. Since the needle is tapered the actual sealing is done at the edge of the hole so you might try a tapered dowel with the compound. I think the seat has a slight chamfer at the hole. I have never seen the needle seat sold anywhere so it is probably not serviced by the user. If all else buy a used carb off of flea-bay.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
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Time Online: 36 days 13 hours 14 minutes
Good comments fellows. Dick, I did "polish" the seat where the rubber tipped valve seats. That made no difference in stopping the overflow. I removed the carburetor from my spare 503 engine (never run) and examined the seat, it is flat on the bottom, no taper or chamfer. Vibration at that RPM could be a problem, so far I checked the engine mounts and they seem firm and no hardware is loose. If vibration is a problem, why doesn't the other carb overflow similarly?
Swapping entire carbs front to back will be something worth trying.
My current plan is to configure the carb from the spare engine so the main jet, needle jet, and idle jet match what I am already using. When good weather arrives (no rain or cold, perhaps Monday or Tuesday), I will install that brand new carb and see what happens. If it works, I will still need to figure out what is wrong with the original carb. This is frustrating.
Any more ideas, I am open to anything at this point.
Paul I checked my needle and seat manually by filling a syringe with fuel and applied pressure while manually holding the needle lever up. It held the fuel back like it supposed to. This should point you to a vibration issue.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
Posts: 1,694
Time Online: 36 days 13 hours 14 minutes
Ace, with the wing tank fuel valve on, carb bowl removed, fuel will run rapidly into where the fuel bowl floats would be. By raising the float arms, I can manually shut off the fuel flow same as you suggest. I will again look for areas of vibration that may be affecting only this carburetor.
I have bent that tab to the point that the engine almost starves for fuel. Adjusting that damn tab for proper fuel flow and shutting off the fuel flow is incredibly sensitive. It shouldn't be like that. I will experiment one more time with bending that tab and if it still doesn't work right, I will replace that carburetor with my spare carb. Most likely I will do this Monday April 23. I will post the results.
Adjusting that damn tab for proper fuel flow and shutting off the fuel flow is incredibly sensitive. It shouldn't be like that.
I totally agree with Paul's point about this. I have had my own issues with carb. fuel level adjustment and float tang's with various motors. I don't know the answer but I sure wish some engineer out there would come up with a better way to adjust float bowl fuel level ! Maybe some sort of screw with an o-ring drilled through the carb. body... Anything besides this bend the tang crap! Just seems like an all around bad way to accomplish an adjustment of such a sensitive nature. JMHO TTT
I suppose you have the bypass pipe between the two overflows on the carbs. My 447 has one with a couple of holes at the bottom to stabilise the float bowl pressure.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
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Time Online: 36 days 13 hours 14 minutes
Yes, the bypass hose is intact, free of obstructions, and has two holes at the bottom. This is where the overflowing fuel exits into free air (and onto my right leg). Yes, this is a horribly crude and awkward method of making float arm adjustments.
Paul: Any chance the leak is in the choke bypass circuit? It takes fuel from the bottom of the float bowl to the carb venturi. Maybe it is opening from vibration or not quite seated. Higher fuel pressure could force its way through???? Joe
Joe's suggestion is worth looking into. It was recommended to me that I disable the choke, and fill the tube with black silicone. The rubber choke seat can get very hard. and leak. It's also possible to turn the seat over and get a "fresh" surface. My problem appeared to be even more bizarre. My bypass hose was weeping, and eventually caused a rich condition that made the engine stumble at higher power settings. After "fixing" what I think was causing the problem, I only got to fly a couple of more times last fall, so I'm not ready to say for sure that it's fixed. In my case the "Float needle clip" was slightly deformed. Instead of the fine wire being rectangular in shape, the bends were slightly opened up. I believe the clip was hooking, or catching on the end of the "float bracket", and not properly closing the "Float needle valve". After reshaping the clip, my engine ran fine. Good luck.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
Posts: 1,694
Time Online: 36 days 13 hours 14 minutes
Overflowing carburetor float bowl problem solved, I found the "smoking gun."!!!
Turns out that the new floats I installed a year ago along with the carb rebuild kit were defective. They lost their buoyancy and floated about 1/8" lower than they should have. They did not sink but were on the way to doing so. What a hell of a deal, those floats cost over $100! And they only lasted a year.
My plan today was to install the new carburetor from my spare engine in place of the problem carb. Before doing that I thought, just for fun, let's compare the floats in the problem carb with those in the non-problem carb. (why didn't I think of that previously There I found the smoking gun, look at the photo. Notice how much lower the floats in the carb bowl on the left are than those on the right. Specifically look at the horizontal and then the vertical pins.
It doesn't take much to make these floats become inoperative. There just isn't enough travel on the float adjustment tab to compensate for the sinking floats. Rather than swap carburetors I simply replaced the floats in the problem carb with those in the new carb.
Up to now I never even considered that the floats, since they were only a year old, were the problem. I just didn't have a good visual reference of how the floats should float and therefore even though I looked at them every time I did the tests I never noticed that they were sinking. Am I old too soon, smart too late?
Engine runs at various RPMs and durations verified that everything was A-OK. Now, when the weather cooperates, I will get back to flying (and writing stories).
Thanks for all your suggestions and concern, I appreciate that. Thanks for your observation about the choke seat. I will check that to ensure that it isn't a contributing problem.
Paul, When I was searching for my problems, I weighed my floats on a gram scale to see if they were the same. I figured that if they were the problem, they would be different. Glad to hear you solved your problem.
I flew with a motorcycle carb on my rotax 277 for a while before learning fuel isn't supposed to spray back in your face and the engine isn't supposed to run that rich. glad you got it under control paul!
Glad its fixed (but something else to worry about). Too bad the Gathering of Eagles is no more, I would have loved seeing your new bird here with the WWI crowd.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
Posts: 1,694
Time Online: 36 days 13 hours 14 minutes
Yes Joe, I will miss seeing the Gathering of Eagles and fun that goes along with it. Sure glad we connected during one of the events. It was my understanding that it was going to be replaced with another event, any word on that? Finally, I do not have a new bird, just the same Hun Fighter AirBike Single built back in 1998. But I will be soon getting back in the air following about 6 months of inactivity.
Yes Joe, I will miss seeing the Gathering of Eagles and fun that goes along with it. Sure glad we connected during one of the events. It was my understanding that it was going to be replaced with another event, any word on that? Finally, I do not have a new bird, just the same Hun Fighter AirBike Single built back in 1998. But I will be soon getting back in the air following about 6 months of inactivity.
Paul
The Gathering of Eagles is moved to Ohio this year at Russ Turners airdrome. Here is his message: As most know, the annual Gathering of Eagles WW1 meeting in Gardner is now over due to loss of EAA support. Marv asked if I could try it out at my field just east of Dayton, 50 OH. We’re shooting for a more limited event for builders and pilots on Saturday, 30 June, 2018. Hope to have an “aero-picnic” for enthusiasts and historians with a couple of presentations on building and WW1 formation flying. Big lunch at the field on Saturday, lots of hotels/restaurants 7miles down at hwy 35/I-71 interchange. Hope to see you noble ladies and gentlemen of the air. And the rest of you, too. More over the next weeks.
There is a group of guys in Kansas who have built a grass strip airport (somewhere near Pleasanton, KS I think). They are trying to organize a replica/ultralight flyin this summer. I will see if I can track down more info.
A/B Plans #112 has 1008 hours as of 02-09-2015 Ace
Posts: 1,694
Time Online: 36 days 13 hours 14 minutes
Whoo-ee! AirBike ace got airborne this afternoon for a 1/2 hour test flight. The carburetor worked well, no overflowing! It was a bit windy with a 7 or 8 MPH direct crosswind at ground level. 10 MPH is the maximum component. The houses and trees bordering the runway create turbulence. Made for a ragged landing. Wind at 1000' AGL was rough and stronger. 30 minutes proved that everything was working well so I came down and will fly more when conditions are favorable.
Bad news, I have been asked to vacate the hangar I rent as the owner wants to store some tractor machinery in there. I am searching for another place to call home; this will be the 5th time in 20 years.
Hope all is well with everyone, remember, the best time to fly is whenever you can!
Charlie, we will be looking forward to whatever news you can bring about the potential for a light plane fly-in. I am gonna miss going to Gardner for the Gathering of Eagles.
Here is what I found: Greetings everyone: A friend of mine at Oshkosh has spoken to a couple of you about our site here in South East Kansas, 16650 60th Road, Erie Ks. As of July 1, 2017 Squadron Field (11KS) has been open for flights! While the hangar is not yet up, the runway has been used by several aircraft, and we are constantly improving. Our next Great War event is the 6th thru the 8th of October 2017. Please feel free to contact me with any questions you may have, and we look forward to you all flying over the trenches!
In The Service Of Honor, Amor vincit omnia, vzfw Steinraud, Kaun Steinrøðarson, Kenneth The Dark, Donatien, (Kenneth Steenrod) 18742 McKinnley Lake Road Parsons Kansas, 67357 USA Home 620-763-2325 Cell 620-778-9577
And this: Greetings: We are having a fly in at Squadron Field, 11KS, on July 1, 2018 if that helps fill things out for the magazine. I can provide more info if you would like.
In The Service Of Honor, Amor vincit omnia, vzfw Steinraud, Kaun Steinrøðarson, Kenneth The Dark, Donatien, (Kenneth Steenrod) 18742 McKinnley Lake Road Parsons Kansas, 67357 USA Home 620-763-2325 Cell 620-778-9577
Whoo-ee! AirBike ace got airborne this afternoon for a 1/2 hour test flight. The carburetor worked well, no overflowing! It was a bit windy with a 7 or 8 MPH direct crosswind at ground level. 10 MPH is the maximum component. The houses and trees bordering the runway create turbulence. Made for a ragged landing. Wind at 1000' AGL was rough and stronger. 30 minutes proved that everything was working well so I came down and will fly more when conditions are favorable.
Bad news, I have been asked to vacate the hangar I rent as the owner wants to store some tractor machinery in there. I am searching for another place to call home; this will be the 5th time in 20 years.
Hope all is well with everyone, remember, the best time to fly is whenever you can!
Charlie, we will be looking forward to whatever news you can bring about the potential for a light plane fly-in. I am gonna miss going to Gardner for the Gathering of Eagles.
Paul Fiebich
Paul sorry to here you’re loosing the hanger...again. I’m sure farm equipment where you live is more profitable to keep than a hun killer. I’m lucky the land owner where my A/B lives is a pilot too. Good luck.
Logged
There I found the smoking gun, look at the photo. Notice how much lower the floats in the carb bowl on the left are than those on the right. Specifically look at the horizontal and then the vertical pins.
