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RUNNING RICH, Cannot Adjust To Lean - CB-119
There may be a time when your engine runs rich and the carburetor cannot be adjusted to the lean side. Too rich is too rich and needs to be fixed. Check the floats first. Remove float cover, lift out float, and shake it. It should be light and dry. If it sloshes with fuel inside it has a crack somewhere. Any fuel inside the float is bad, making it sink and fuel level goes too high (making it run rich, or fuel overflows).
If there is fuel in the float, put it in a pan of hot water, weigh it down to stay submerged, heat gently (not boiling the water) until it bubbles out where you will see location of the crack. Continue with gentle heat until all of the fuel inside boils off as vapor and it stops bubbling. Remove float from water BEFORE cooling. Allow to cool, then solder up the crack. A leaking waist joint can easily be soldered. For a crack in an open surface, solder on a thin brass patch. A crack near or on a corner can be difficult to repair. Otherwise replace the float.
When floats are sealed and don't slosh, check float level. Set at 7/16 inch per the book. When you get it right fuel level should be right at top of main jet where you can see it, but not overflowing the bridge in the carb throat. If you still can't adjust it to run a bit lean, then check the needle. Needle has a shoulder that should be flush with bottom of the air piston. If too high, loosen the set screw and pull the needle down until shoulder is flush. Also check the number on the shank of the needle to be sure you have the right needle for your application.
If correct needle, and the needle shoulder is flush and it's still running rich, you can try setting the needle shoulder 1/32 inch below flush (slightly exposed). That's equal to about 2/3 turn on the adjusting nut. This can compensate for a worn needle or worn jet. If it still runs rich, then you may need to replace the needle or jet (or both). They are not supposed to wear, but if it has been assembled with the main jet off center it can rub wear.
See video Centering the Jet.