Fuel leaking on 140A

[5060]

Working on a 140A with fuel dripping from the carb with a drop every 20 seconds or so. Stromberg was overhauled in 2018. Fuel is dripping from the middle of the carburetor, even when the fuel selector is in the off position. I am suspect of the fuel selector valve, but don't want to just start pulling components for overhaul. I see entries in the forum where fuel may leak thru the carb if the selector valve is leaking. With selector in the off position, there is also a drip from the fuel gasolator drain when opened. Carb or selector valve? Old A&P needs help!

[6898]

Lots of past posts on that, what I've read says Stromberg's leak more than Marvel's . The original fuel valves can be repaired and do leak, we stopped both problems with new style fuel valve and a Marvel carb. There still cheaper than most to fly. Under Links on this home page then members products is the valve we installed 15 years ago still the best thing we did.

[5060]

Yep, and thanks - read many previous posts. This is not the typical Stromberg drip that was corrected with the overhaul in 2018. This is a drip off the bottom of the main discharge nozzle as if the float is 'sunk', but I don't want to pull the carb if the pressure from a leaking fuel valve could be the issue. Owner does not want to go to Marvel and new valve is not his favorite option $$$$. So looking for advice on whether the leaking fuel valve can bypass the float needle and overflow into the discharge nozzle. Diagrams and my experience is that the needle valve should stop the flow even if the selector is leaking.

[6183]

Sounds like you're on track with the carburetor issue, a problem with the float would certainly allow fuel to keep flowing into the float chamber causing an overflow. In any event the carburetor float level needs to be checked. In the Neal Wright articles on this website at the bottom of the forum pages, Neal gives an excellent explanation on the workings of the Stromberg carburetor and how the float level is adjusted. If you have time take a look at the article, it's quite good.

As for the fuel valve you can easily test it by turning the selector to the off position, then remove the flex hose from the carburetor and place it in a container. If fuel still weeps through in the off position, the valve needs attention.

No guarantee, but you can remove the valve and disassemble the unit to see if there is galling or wear grooves in the valve interior body or on the spindle cone. Take care when removing the valve top, there's a small spring and spring washer located under the packing that can prove to takeoff if one's not careful. I would suggest using fine grit valve grinding paste to remove/polish any imperfections in the cone and valve body surface. Just make sure to completely remove the paste once you finish. I checked the valve in my 140A by adding fuel to the ports to see if it leaked through. I believe that the MS29513-109 O-Ring will work as a packing replacement in place of the Cessna p/n 0413020-4 which has been superseded. Several individuals have also utilized the O-Rings in a NAPA #2-12085 as a packing substitute.

[6643]

You have two problems. The shutoff valve should shut the fuel off to the carb. If that works, there won't be any fuel so sustain a leak at the carb.

The shutoff valve cannot make the carb leak. On the other hand, the float valve in the carb should prevent a leak if the fuel valve is left on, or fails. However, this is a known issue with the Strombergs.

It may be worthwhile to open the carb and see if there is something obvious contributing to the leak, and to discern what type of float valve you have. First order of business, however, is to get the shutoff valve working.

[5060]

Thanks to each for the input and experience. The fuel valve is pretty badly grooved on both the cone and body of the original valve. Polished with valve lapping compound but did not try to remove all the grooves. reinstalled but it still has a slow drip when in the Both Off Position. Owner will decide any next steps.
I've studied extensively the information in Neal's pages and others on the forum and have done a little work on my own 140 carb on the C-85. No leaks on mine (N76633), thankfully. I have the carb off the 140A C-90 engine now, but more I study, more hesitant I get to dig too deeply. Does anyone have the float level tool and needle seat tool described in Neal's article that maybe I could borrow or rent for a little while? I plan to open the carb today and see if there is anything obvious in the float chamber, and check and see what needle and seat were installed when the overhaul that was done in 2018. Then decide whether to try to go any further if that is needed.
Does anyone know of an overhaul facility that is still doing Stromberg NAS3A1 carbs? Two that I checked say they are not accepting any carburetors.
And thanks again for the input - all appreciated.