491588S 491588 Air Filter for 4915885 399959 4101 5043 5043A 5043D 5043H 5043K Flat Cleaner Cartridge 3.5-6.5 Hp Quantum Engines Lawn Mower Parts

What It Is

This is a replacement air filter cartridge designed for small engines, specifically 3.5 to 6.5 HP Briggs & Stratton Quantum and similar flat-head engines used in walk-behind lawn mowers. It traps dirt and debris before they enter the carburetor, protecting engine performance and longevity.

Fitment & Compatibility

Before buying, check your engine’s model and series. This filter fits Briggs & Stratton Quantum engines (and some non-Quantum) with a flat, rectangular air cleaner housing. Key OEM cross-references include 491588S, 491588, 399959, 5043, 5043A, 5043D, 5043H, and 5043K. Measure your old filter: this cartridge is roughly 3.5 x 1.5 x 1.5 inches. It will not fit round or cylindrical air cleaner assemblies, nor engines requiring a pre-filter or foam wrap. If your mower’s air cleaner housing has a metal or plastic cover that snaps or screws over a flat filter, this is likely correct.

Key Things to Know

• Quality note: This is an aftermarket filter, not OEM Briggs & Stratton. It typically matches OEM specs but may have slightly different foam density or pleat count. It’s fine for regular mowing, but if you operate in heavy dust, consider OEM for tighter filtration.
• Installation: Very easy—no tools required. Remove the air cleaner cover, pull out the old filter, drop in the new one (flat side facing the engine), and reattach the cover. Ensure the filter seats fully to avoid unfiltered air leaks.
• Common gotcha: Some Quantum engines use a different filter (round or with a foam pre-cleaner) even if the housing looks similar. Always verify the housing shape and check your engine’s model number (e.g., 12A-xxx) against the cross-reference list.
• Replacement interval: Replace every 25 hours of use or annually, more often in dusty conditions. A dirty filter causes hard starting, rough idling, and reduced power.

Should You Buy It

If you have a Briggs & Stratton Quantum or compatible flat-head engine (3.5–6.5 HP) and need an affordable, easy-to-install air filter for routine maintenance, this is a solid choice. It’s not for heavy-duty or commercial use, but for home lawn mowing, it delivers reliable filtration at a low price. Just double-check your engine’s housing shape and model number first.