Small Engine

Honda GX120

4-Stroke

The Honda GX120 is a 118cc 4-stroke overhead-valve small engine built on Honda's GX commercial platform, powering pressure washers, water pumps, tillers, go-karts, and generators. The entry point of the GX series, it is designed for light to moderate duty applications where compact size and reliability are paramount. It uses a Keihin float-type carburetor and accepts NGK BPR6ES or Champion RC12YC spark plugs. The overhead-valve design provides superior fuel efficiency and longevity over flat-head designs. Routine maintenance: annual oil change (SAE 10W-30), air filter, and spark plug.

See a wrong fitment? Report a correction.

Verify before ordering: Fitment can vary by serial number, production date, region, and sub-model. Match the OEM number and physical dimensions before ordering.

Equipment: Small Engine · 4-Stroke
Covered Parts: Spark Plug, Air Filter, Carburetor, Fuel Filter
OEM References: 98079-55846, 17210-ZE0-505, 16100-ZH7-W51, 16955-ZE1-010
Model Family: GX120, GX140, GX160, GX200
Last Reviewed: 2026-05-20
Data Confidence: Aftermarket-confirmed
Sources Consulted: OEM part references, Aftermarket catalog cross-references, Retailer fitment listings

ℹ See also: GX140, GX160, GX200 — parts are often interchangeable within this family.

Quick Fitment

Part Type	OEM / Spec	Common Option	Confidence
Spark Plug	98079-55846	NGK BPR5ES	Medium · 2026-05-20
Air Filter	17210-ZE0-505	Stens 100-958	Medium · 2026-05-20
Carburetor	16100-ZH7-W51	Stens 520-702	Medium · 2026-05-20
Fuel Filter	16955-ZE1-010	Stens 120-327	Medium · 2026-05-20

Tune-Up Kit

Common service bundle: spark plug, air filter, carburetor, fuel filter.

Maintenance Interval

Inspect filters and fuel lines each season, replace spark plugs during annual service, and service carb/fuel-system parts when starting or idle symptoms appear.

Before You Buy

Confirm the full model is Honda GX120, not just the family name.
Check serial number, production date, and regional variant before ordering.
Match the old OEM number stamped on the removed part when available.
Compare dimensions, plug gap, thread, fuel line diameter, or chain pitch/gauge where applicable.

Common Mistakes

Ordering from a family listing without checking the exact sub-model.
Buying a kit that includes the headline part but wrong gaskets, lines, or bulb size.
Choosing the wrong carburetor revision when multiple versions were used.
Installing the correct plug number with the wrong gap.

Symptoms Map

Won't start

Spark plug, fuel filter, primer bulb, carburetor

Starts then dies

Fuel filter, fuel line kit, carburetor

Bogs under throttle

Air filter, carburetor, spark plug gap

Replacement Options

Best OEM equivalent

Start with OEM references 98079-55846, 17210-ZE0-505, 16100-ZH7-W51, 16955-ZE1-010 and match the removed part before choosing a listing.

Common aftermarket option

Cross-check aftermarket listings such as NGK BPR5ES (spark plug), Stens 100-958 (air filter), Stens 520-702 (carburetor) against the OEM number and dimensions.

Best for annual tune-up

Bundle spark plug, air filter, fuel filter when servicing the Honda GX120 at the start of the season.

Best if replacing fuel system

Compare the carburetor, fuel filter together so line routing, bulb size, filter style, and carburetor connections match.

Best budget kit

Use kit listings only when every included part matches this model page; cheap kits often mix correct headline parts with wrong bulbs, lines, or gaskets.

FAQ

Does this fit GX140 or GX160? Parts may interchange with GX140, GX160, GX200, but verify the serial range, OEM number, and physical part details before ordering.

Should I buy OEM or aftermarket parts for the Honda GX120? Use OEM when the part controls fuel metering, ignition, or safety. Aftermarket kits can be useful for routine filters, bulbs, plugs, and tune-up bundles when the OEM number and dimensions match.

How do I avoid ordering the wrong carburetor for the GX120? Match the carburetor number stamped on the removed unit, then compare linkage, choke setup, primer routing, gasket stack, and fuel-inlet direction.

What should I check before replacing fuel-system parts? Photograph the old fuel-line routing, match line diameter and filter style, and compare primer bulb size before buying a kit.

Spark Plug

OEM98079-55846Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Dimensions: 0.7-0.8mm gap
Variant notes: NGK BPR5ES equivalent; used in water pumps, pressure washers, tillers, and compactors

Brand	Part #
NGK	BPR5ES	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.
Champion	RS12YC	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Air Filter

OEM17210-ZE0-505Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Paper element; also fits GX110. Superseded by 17210-ZE0-822

Brand	Part #
Stens	100-958	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Carburetor

OEM16100-ZH7-W51Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Keihin BE60B float-type carb; fits GX110 and GX120

Brand	Part #
Stens	520-702	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.
Keihin	BE60B	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Fuel Filter

OEM16955-ZE1-010Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: In-tank fuel filter/joint; fits GX series 4-13HP engines

Brand	Part #
Stens	120-327	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.