I start out by completely disassembling the carburetor and cleaning it. You must be very careful when pulling the two halves of the carburetor apart. The idle tube inside is very delicate and easily bent or broken. Pull them straight apart, without twisting or canting the pieces. When I take the carburetor apart, I look carefully at the felt dust seals where the throttle and choke shafts pass through the carburetor casting. If they are extremely dirty or deteriorated, I will remove them and their retainers. The retainers normally get damaged in this process. If the idle tube won't come out easily, leave it in. Then I put all the metal parts, except the float, in a product called Chem-Dip Carburetor and Parts Cleaner. It comes in a gallon, paint-type can with a metal basket in it. You should be able to find it at any good auto parts store.
Put the parts in the basket and submerge them to soak according to the label directions. When I take them out, I rinse them with clean water and let them dry. Then, I clean up the castings and the other parts with toothbrush-style nylon, stainless steel and brass brushes. Some folks use soda blasting to clean up the castings. This cleaning includes the two shafts and butterfly plates. Make sure you remember which way the plates come off, so they go back on correctly. I run a thin, soft copper wire through all of the orifices to make sure they are clear. After everything is clean I reassemble everything using the new dust seals and retainers (if needed) and new gaskets. I normally replace all the screws with stainless steel screws, also. You should be able to find them at any good hardware store or fastener place. I use a thread sealant on the threads of the discharge nozzle and needle valve cage when reassembling to prevent fuel leakage at these points. I use a gasket sealant on the main metering jet gasket. Use just a very small amount at each location, so that you don't plug any orifices.
This is the thread sealant I use.
And this is the gasket sealant I use.
They are both gasoline resistant if you let them cure properly before introducing fuel.
Set the float according to the following diagram. Set the idle adjusting screw and the throttle stop screw in accordance with the Operator’s Manual. Put it all back together and try it out. You may have to make several attempts to get the float adjusted just right.
You will also likely need to adjust the rod between the carburetor and the governor rockshaft. This procedure is covered in the Governor section of the Fuel System chapter of the GSS-1411 Blue Ribbon Service Manual.
The part numbers and quantities that you may need are:
251235R1 – Carburetor/Manifold Gasket (1)
251337R3 - Fuel Bowl Gasket (1)
25948D - Needle Valve Cage Gasket (1)
45148D - Dust Seal Retainer (3)
45149DA - Dust Seal (3)
47401D - Discharge Nozzle & Main Metering Jet Gaskets (2)
Other parts may need to be replaced if they are worn, damaged or missing. This includes the float, main metering jet, idle tube, inlet screen, etc.
Check the fuel inlet threads and the mounting flange threads carefully. If they are damaged, they can be repaired using a helicoil kit of the appropriate size. Several board members are set up to provide this service if you need it.
