Primer Bulb 694394 Replacement for Briggs & Stratton 4178 494408 5084 Lawn Mower Carburetor

What It Is

This primer bulb (model 694394) is a fuel system component that manually pushes fuel into the carburetor for easier engine starting. It’s designed for small engines, primarily walk-behind lawn mowers, but also fits snow blowers, generators, and pressure washers using compatible Briggs & Stratton engines.

Fitment & Compatibility

Before buying, check these specifics:

• OEM cross-references: Replaces Briggs & Stratton part numbers 694394, 4178, 494408, and 5084. Verify your engine’s part number or look for these on the old bulb.
• Engine models: Fits many Briggs & Stratton single-cylinder engines (e.g., 12H800, 12L900, 12M800, 12P700, 12Q900, 12R800, 12S800, 12T800, 12U800, 12V800, 12W800, 12X800, 12Y800, 12Z800, 13A800, 13B800, 13C800, 13D800, 13E800, 13F800, 13G800, 13H800). Check your engine’s model number (stamped on the blower housing or valve cover).
• Physical dimensions: Bulb diameter is approximately 0.75 inches; stem length about 0.5 inches. Measure your old bulb’s stem diameter (should be ~0.25 inches) and ensure the mounting hole in the carburetor or fuel cap matches.
• Aftermarket note: This is a non-OEM replacement. It should work fine for most, but if you need an exact OEM match (e.g., for warranty or precise fit), buy from a Briggs & Stratton dealer.

Key Things to Know

• Quality: Generally good for the price—users report it holds prime well and is durable for a season or two. Some report slightly softer rubber than OEM, but function is unaffected.
• Installation difficulty: Easy (1/10). Pull off the old bulb, push in the new one. No tools required for most applications. If the old bulb is stuck, use a small flathead screwdriver to gently pry it out.
• Common gotchas:
  • The bulb may fit tightly at first; warm it in hot water for 30 seconds to soften the rubber.
  • If the carburetor is dirty (varnish, debris), the new bulb won’t solve starting issues—clean or rebuild the carb first.
  • Ensure the mounting hole is clean and free of old gasket material before installing.
• Check for cracks: If the old bulb has cracks or leaks, replace it immediately to avoid fuel spillage and fire risk.

Should You Buy It

Buy this if you have a Briggs & Stratton engine with part numbers 694394, 4178, 494408, or 5084, and the old bulb is cracked, hard, or not sealing. It’s a budget-friendly, easy swap that restores reliable priming. Avoid if your engine has a different carburetor design (e.g., some newer engines use a primer button instead of a bulb) or if the carburetor itself is damaged—replace the carb in that case.