Note: Obtain a clean pan for parts before beginning the disassembly process
Disassembly Instructions
Remove Linkage: Remove the pin spring and choker link washer (A). ne-chip>
Remove Hardware: Remove the body attaching screws (B). ne-chip>
Separate Castings: Hold the carburetor in your right hand with the flange facing up. With your left hand, carefully pull off the top casting. Take extra care when the pump piston emerges so that it does not catch on the body gasket (C) and tear it. ne-chip>
Remove Gasket: Remove the body gasket (C).
Remove Push Rod: Remove the step-up push rod (G).
Remove Float Mechanism: Remove the float lever pin and plug assembly (D), then remove the float and lever assembly (E).
Remove Needle Valve: Remove the needle and seat assembly (F).
Remove Step-Up Valve: Use a screwdriver to remove the step-up valve assembly (H).
Clean Orifice & Valve: Remove the power orifice (I) from the step-up valve assembly. Be careful not to lose the internal spring and ball (J). Wash these components in clean gasoline, blow out the power orifice with compressed air, and reassemble them immediately to prevent losing the small parts. ne-chip>
Clean Pump Valve: Remove the pump valve assembly (K), wash it in gasoline, and blow it out with air. ne-chip>
Clean Check Valve: Remove the check valve assembly (L), wash it in gasoline, and blow it out with air.
Clean Vent Tube: Remove the vent tube (M), wash it in gasoline, and blow it out with air.
Clean Idle Jet: Remove the idle jet tube (N), wash it in gasoline, and blow it out with air.
Clean Nozzle: Remove the nozzle (O), wash it in gasoline, and blow it out with air.
Clean Metering Screw: Remove the main metering screw (P), wash it in gasoline, and blow it out with compressed air through the hole in the end.
Clean Idle Passage: Remove the idle passage tube (Q), wash it in gasoline, and blow it out with air.
Remove Plug: Remove the idle hole plug (R).
Remove Adjuster: Remove the idle adjustment screw (S).
Clean Piston Assembly: Remove the step-up piston plug (T), step-up piston (U), and step-up piston spring (V). Wash these parts in gasoline and blow them out with air.
Final Body Wash: Wash the main carburetor body thoroughly in gasoline and blow out all internal passages with compressed air. Repeat this operation at least once to ensure all foreign matter has been completely removed.
Important Service Note: Do not remove the throttle valve and shaft unless they are badly worn and require replacement.
Reassembly Instructions
Replace Adjustment Screw: Reinstall the idle adjustment screw (S) into the upper hole.
Replace Hole Plug: Reinstall the idle hole plug (R) into the lower hole.
Reassemble Piston: Replace the step-up piston (U), step-up piston spring (V), and step-up piston plug (T).
Replace Passage Tube: Reinstall the idle passage tube (Q).
Replace Metering Screw: Replace the main metering screw (P).
Note: When servicing BB1, BB1A, 2455, and 245SA units, replace the main metering screw and needle assembly as a single unit.Replace Nozzle: Replace the nozzle (O), making sure it is screwed down tight against its gasket.
Replace Jet Tube: Reinstall the idle jet tube (N).
Replace Vent Tube: Reinstall the vent tube (M).
Replace Check Valve: Replace the intake check valve assembly (L).
Replace Pump Valve: Replace the pump valve assembly (K). Verify that the internal ball inside the pump valve moves completely freely.
Replace Float: Reinstall the float and lever assembly (E) along with the float lever pin and plug assembly (D).
Replace Needle & Seat: Reinstall the needle and seat assembly (F).
Set Float Level: Establish the correct float level by carefully bending the lip on the float lever if necessary:
Standard Units: Set flush to 1/32" below the top surface of the casting. Gauge this measurement from the top surface of the float, not from the soldered seam. ne-chip>
BB1, BB1A, 2455, and 245SA Units: Set the float level between 1/32" and 1/16" below the edge of the casting. ne-chip>Replace Push Rod: Reinstall the step-up push rod (G). Ensure the rod is oriented with its small end pointing downward.
Replace Body Gasket: Position the body gasket (C) back in place.
Join Castings: Reassemble the upper and lower castings together. Carefully insert the pump piston into its cylinder, ensuring that the step-up push rod (G) successfully enters the hole in the step-up piston plug (T) and that the idle passage tube (Q) enters its corresponding hole in the lower body.
Secure Screws: Replace the body attaching screws (B) and tighten them down evenly and securely.
