O-200A Fuel leak from carb

Chilito

Chilito

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Chilito
Went to the hangar today, pulled the plane out, big fuel leak dripping from the carb. It was not leaking sitting in the hangar -- it started when I moved the plane. So I think something came loose. But what? Shut off the fuel and it stopped. Turned it on, leak started up again. What are the possibilities? Needle and seat issue? Entire carb overhaul?

It is a Marvel-Schebler MA-3SPA, overhauled in 2012 and has about 410 hours on it.

Thanks all, your perspectives are appreciated!
 

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Could be a needle not seating properly. Go to this page and scroll down to "Neil Wright on the Stromberg." You undoubtedly have a different model, maybe even something other than a Stromberg/Bendix, but some of this might be similar.

Strombergs do have a tendency to leak; we call the "Stromberg drool" in the Fly Baby world.

My A&P told me, that if my carb seemed to be leaking, to whack it once or twice with a rubber hammer or piece of wood to try to jar the needle and get it to seat. YMMV.

Ron Wanttaja
 
Looks like a Cessna 150, which will have a Marvel Schebler (Marvelous Dribbler) carb on it, or one of the descendants of that horrible thing. Most likely a float needle valve with something holding it open. Best to take the drain plug out of the back bottom of the carb, put a bucket under it and turn the fuel on to try to flush it out. Ground that bucket to the airplane and to ground. Don't do this in a hangar. Put the plug back in, but it's a 1/8" NPT plug that will split that bowl if you overtighten it. Make sure there's no sealant left in that hole before the plug goes in. If the flushing doesn't fix it the carb has to come off and get fixed. Could be a bad float, even.

None of this is owner-maintenance.
 
Update: Following Ron's advice, I gave it a whack with the rubber grip of my hammer and the leak stopped.
 
Dan Thomas said:
Wrong term. I should have said float valve. The needle is the idle mixture valve.
Click to expand...
The term for a needle is some thing that meters.
A valve some the that turns a fluid on or off.

The float Valve simply turn the flow on or off.
A needle regulates flow, (by allowing a certain quantity to pass a certain area in a certain time).

Needle = regulation
Valve = on or off

OBTW-- there are no needles in a MA3- Carb it is done with set size orifices
 
Chilito said:
Update: Following Ron's advice, I gave it a whack with the rubber grip of my hammer and the leak stopped.
Click to expand...
If it cured the leak, you need a new carb. because the float is touching the side of the carb bowl, is it is the float is loose on its pivot point.

the C-150 is famous for that.
 
Chilito said:
Went to the hangar today, pulled the plane out, big fuel leak dripping from the carb.
Click to expand...

That was more like flow than a leak. It's good the hammer cure worked, but taking the aircraft out of service until the carburetor is replaced is a really good idea.
 
Dan Thomas said:
Wrong term. I should have said float valve. The needle is the idle mixture valve.
Click to expand...
Huh. Dun learnt something today. For the last 53 years I been calling the pokee bit and the place where it gets poked into the "needle and seat"...
 
Capt. Geoffrey Thorpe said:
Huh. Dun learnt something today. For the last 53 years I been calling the pokee bit and the place where it gets poked into the "needle and seat"...
Click to expand...

I learnt somethin' too ... I was taught it was a needle & seat but (thanks to POA) I know it's a "float valve assembly" that looks just like a needle and seat - o_O
233-615-F_34.jpg

Dale
 
Chilito said:
Update: Following Ron's advice, I gave it a whack with the rubber grip of my hammer and the leak stopped.
Click to expand...
Unless it happens when it is not looking, they do it best late at night..

cleans the hangar floor really great. got any timers turned on ? sssst zap

Got idea--- turn off the fuel:)
 
I had the screws holding up the float bowl to the top plate of the carb get loose. When it happened it would leak some but it also caused no RPM decrease with Carb heat. Tightened the screws problem went away. Added locktite to the screw threads and problem never came back.
 
William Pete Hodges said:
I had the screws holding up the float bowl to the top plate of the carb get loose. When it happened it would leak some but it also caused no RPM decrease with Carb heat. Tightened the screws problem went away. Added locktite to the screw threads and problem never came back.
Click to expand...

They had a problem with that. https://msacarbs.com/pdf/MSA-14.pdf
 
Capt. Geoffrey Thorpe said:
Huh. Dun learnt something today. For the last 53 years I been calling the pokee bit and the place where it gets poked into the "needle and seat"...
Click to expand...
So do most of us. ANd most of us know what we're saying. But Tom is aware that some carburetors did actually have a needle that moved in an orifice to meter fuel to the nozzle. They were common in cars, and were called the power valve. Tom might have seen them in carbs on radials.
 
Dan Thomas said:
some carburetors did actually have a needle that moved in an orifice to meter fuel to the nozzle. They were common in cars
Click to expand...
Yup. Carter YFA carbs used them for the main metering system (used to work on those for a living), a lot of the constant velocity carbs (like the Bings on my Rotax) have a metering needle in the main jet, etc.
 
Capt. Geoffrey Thorpe said:
Yup. Carter YFA carbs used them for the main metering system (used to work on those for a living), a lot of the constant velocity carbs (like the Bings on my Rotax) have a metering needle in the main jet, etc.
Click to expand...
Are we still talking about the MA3SPA on the C150, or have we changed the subject? Again?
 
Tom-D said:
That doesn't mean you should use them.
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I'm talking about carbs that were bought and installed that hadn't been assembled properly. Their screws came loose. That service bulletin is from 2008, and affected carbs were built a year or two before that. I had two or three of them show up. Many are still in operation; it's not as if carbs get replaced every year or two. Many are installed at engine overhaul and are there for 20 or 30 years or more. There have been others on this forum complain of leaks at that gasket, so affected carbs are still out there.
 
43.13 Performance rules (general).
(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.
 
Oh joy, another thread of
"he answered in that thread, and I can't have that. Must beat him down"
The audience never tires of that one.
Anyone got some unemployed 10 year-olds we could toss in the mix?
 
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