594281 Primer Bulbs Compatible with 300E 450E 500E 550E 08P502 09P6S 09P7 Series Primer Carburetor Lawn Mower

What It Is

This primer bulb assembly (part 594281) is a replacement fuel-system component for certain Briggs & Stratton and other small-engine lawn mowers. It pushes fuel into the carburetor on startup, eliminating the need for repeated pulls. It’s designed for 300E, 450E, 500E, 550E, and 08P502, 09P6S, 09P7 series engines with a specific primer carburetor.

Fitment & Compatibility

Before buying, confirm these three things:

• Engine model/series – Works only with the listed 300E, 450E, 500E, 550E, and 08P502, 09P6S, 09P7 series. Check your engine’s model number (stamped on the blower housing or valve cover).
• Primer bulb type – This is a direct-fit replacement for the round, push-button style primer bulb on those carburetors. It will not fit older metal-bowl or diaphragm-style carbs without the same bulb housing.
• Measurements – Bulb diameter is about 0.75 inches; the stem length is 0.5 inches. If your original bulb is larger or has a different stem shape, it won’t match. No deck size or brand (MTD, Troy-Bilt, etc.) matters—only engine series.

Key Things to Know

• Quality – Aftermarket at a budget price. Users report it works, but some bulbs are slightly stiffer than OEM. Expect a functional, not premium, feel.
• Installation – Very easy (5 minutes). Pull off the old bulb, push in the new one. No tools needed. Make sure the stem fully seats into the carburetor grommet.
• Common gotcha – If the bulb doesn’t snap in securely or feels loose, the grommet inside the carburetor may be worn. Replace that grommet (often sold separately) to avoid air leaks.
• Durability – Some bulbs crack after a season in direct sun or heat. Store mower covered if possible.

Should You Buy It

If you own one of the listed engine series and your primer bulb is cracked, torn, or won’t hold a prime, this is a cheap, quick fix. It’s right for DIY homeowners who want a simple repair without buying a whole carburetor. Skip it if you need an OEM part for exact feel or if your carburetor grommet is also damaged—order both at once.