594605 Carburetor for Briggs Stratton B&S Nikki 594601 33R777-0003-G1 33R777-0004-G1 31P977-0635-E1 331777-0901-B1 331777-0946-B1 21B807-2453-B2 with Spark Plug and Fuel Pump

What It Is

This is a complete replacement carburetor kit for select Briggs & Stratton engines, designed for lawn mowers, tractors, and other outdoor power equipment. It includes the carburetor itself, a spark plug, and a fuel pump, making it a convenient all-in-one service set for common small-engine tune-ups.

Fitment & Compatibility

Before buying, verify your engine’s model, type, and code numbers (e.g., 33R777-0003-G1, 31P977-0635-E1, 21B807-2453-B2) stamped directly on the engine shroud or valve cover. This carburetor replaces OEM numbers 594601, 594605, and Nikki-style units. It fits specific B&S engines from the 21, 31, and 33 series—not all models. Check that your mower deck size and brand (e.g., Craftsman, Troy-Bilt, Husqvarna) are compatible, as mounting bolt spacing and fuel line diameter can vary. Measure your old carburetor’s flange width and bolt pattern if unsure.

Key Things to Know

• Quality variance: Aftermarket carburetors like this may have slightly different jetting or gasket thickness than OEM, which can affect idle or fuel mixture. Expect to adjust the carburetor after installation.
• Installation difficulty: Moderate—requires basic hand tools (socket set, screwdrivers) and careful linkage routing. Watch for small springs and gaskets that can be easily lost.
• Common gotcha: The included spark plug may not match your engine’s heat range or gap spec. Always double-check the gap (typically 0.030") and compare to your existing plug.
• Fuel pump integration: The fuel pump is usually a separate diaphragm unit; ensure all vacuum lines and fuel lines are reconnected correctly to avoid air leaks or flooding.

Should You Buy It

This kit is a solid budget option for DIYers who need a quick, complete carburetor swap on a compatible Briggs engine and are comfortable with basic adjustments. However, if you prioritize exact OEM fit and long-term reliability, consider spending more on a genuine Briggs & Stratton carburetor instead.