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Carburetor Work

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bob turner

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It has been a quarter century since I had to mess with a carburetor - other than the M-S that fell apart on approach to Pecos on a 90 degree day (I was already too old for that nonsense).

So a buddy was having problems with his Stromberg - I volunteered to help, so I found my old test setup and tried to get the darn thing set up. It sort of worked at first, but once in a while it leaked. Then, watching it, it would fill all the way to the rim, and the float would not move.

Tried a different float - worked fine (yes, I re-lapped the needle first thing). Puzzling. So i weighed both floats -40 grams on the good one; fifty on the one having a hard time. That's a lot - 25% heavier!

Beaver Bill sent us a float (thanks, Bill) and with some serious fitting and polishing in the needle slot and its corresponding pin in the float, I got ten good trials in a row today. That does not mean we are home free - there is still the airplane system to hook up (it is a CSA Aeronca L-3) and a full power runup (I insist). But it is worth typing about.

Folks with good ears could hear fluid sloshing around inside the heavy float. I could not find a leak.

The carburetor had come with a fresh professional overhaul, and I got involved because it seriously leaked.

Anyway, it was a nice refresher course in setting float levels and polishing needles.

Take-aways:

The all-stainless needles appear to all need slot work. It should look like a mirror in there, and it should fit freely in the float. Old floats can have ridges on the pin; make sure the needle can move freely side to side on the pin, especially at the top of the slot.

Pay attention to the washer thickness under the seat. I wound up with .070 to get a fluid level of 13/32. Took multiple trials after I got the needle and float working properly.

Don't lose the little set screws. The top one is 8-32; the side is 10-32. If they fall on the shop floor you have to make new ones.

Double-check the safety wire - it cannot interfere with any moving parts.

Do not assume that professional rebuilders will spend several hours making sure all this works properly.

And - best of all, if you do it right, and you only own one airplane, a quarter-century will go by before you need to do another. Sure, you might have to clean the passages now and then, but once fixed, no leakee.
 

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