Yesterday's Tractors - Step by Step Carburetor Overhaul

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Not just any socket will fit in the space around the Main Nozzle. I've had good luck with a 1/4" drive deep socket. It seems to have a pretty thin wall.

Set the discharge Main Nozzle aside. Discard the little round gasket, after checking that its replacement in the rebuild kit is the correct size.

In the cavity next to the Main Nozzle is the main jet burried way down in there. It's another one of those straightslot screwdriver jobs again. Pick the widest screwdrive that will fit the slot, secure the lower body casting from moving around and apply constant even pressure on the screwdrive to keep it from slipping and out it will come. If you should gall it up, buy a replacement. Again, annoying, but not too expensive.

You want to check the upper body mating surface for flatness by moving a steel rule all around the mating surface. If there is more than 1/2 of a gasket's thickness difference between the center and outside edges, plan on reassembling the carburetor with two gaskets.

By now the Upper body has cooked enough in the carburetor cleaner. Pull the parts basket out of the soup and let it drain (you've got your safety glasses on and protecting your hands, right?). The carb cleaner is, in fact, water soluable but it is nasty stuff. I use spray brake cleaner instead of water to clean all that nasty stuff off of the clean carburetor parts. But the real necessity is compressed air. If you do not have compressed air, you will be lucky to get a satisfactory rebuild. The hidden passages in the carb is where all the varnish build-up is hiding, and while the parts cleaner will soften that stuff, it is the compressed air that forces the gooey mess out of the passages where the brake cleaner can dissolve it. Hit it with brake cleaner then hit all the passages with air. Repeat until that casting is Spic 'n Span clean, then set it aside on a nice clean cloth. (Anybody actually remember Spic 'n Span?)

Place the lower body, main jet, and discharge nozzle into the parts basket and lower it into the carburetor cleaner soup.

After the upper body is thoroughly clean and dry, it is time to replace the throttle shaft. 99% of old carburetors leak air around the throttle shaft and that upsets the air-fuel mixture something terrible. The throttle shaft is made of brass and is the part that wears, the throttle body bore is usually unaffected.

To get the shaft out of the throttle body, you have to remove the butterfly valve. It is retained by (you guessed it) 2 brass straightslot screws. Secure the shaft so it won't move and keep the screwdrive from slipping, and they, too, will come out.

Note the stampings on the butterfly valve so that you can reinstall it exactly as it came out of the throttle body. Make sure that the rebuilt kit has replacement screws, and throw the old ones away.

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