Small Engine

Honda GX390

4-Stroke

The Honda GX390 is a 389cc 4-stroke overhead-valve engine and the top model in Honda's single-cylinder GX commercial series, powering large pressure washers, high-output generators, log splitters, and construction equipment requiring sustained torque. It uses a Keihin float-type carburetor and accepts NGK BPR6ES or Champion RC12YC spark plugs. Oil quality and change intervals are critical at this displacement — Honda specifies SAE 10W-30 with changes every 100 hours. The Keihin carburetor float level and main jet are the primary fuel system service points. One of the most widely remanufactured small engines in North America.

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, Recoil Starter, Ignition Coil
OEM References: 98079-56846, 17210-ZE3-505, 16100-ZF6-V01, 28400-ZF6-003ZA, 30500-ZF6-W31
Model Family: GX340, GX390
Last Reviewed: 2026-05-20
Data Confidence: Aftermarket-confirmed
Sources Consulted: OEM part references, Aftermarket catalog cross-references, Retailer fitment listings

ℹ See also: GX340 — parts are often interchangeable within this family.

Quick Fitment

Part Type	OEM / Spec	Common Option	Confidence
Spark Plug	98079-56846	NGK BPR6ES	Medium · 2026-05-20
Air Filter	17210-ZE3-505	OEM 17210-ZE3-505	Low · 2026-05-20
Carburetor	16100-ZF6-V01	Keihin HA-Y	Medium · 2026-05-20
Recoil Starter	28400-ZF6-003ZA	Stens 150-472	Medium · 2026-05-20
Ignition Coil	30500-ZF6-W31	OEM 30500-ZF6-W31	Low · 2026-05-20

Tune-Up Kit

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

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 GX390, 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

Bogs under throttle

Air filter, carburetor, spark plug gap

Replacement Options

Best OEM equivalent

Start with OEM references 98079-56846, 17210-ZE3-505, 16100-ZF6-V01, 28400-ZF6-003ZA and match the removed part before choosing a listing.

Common aftermarket option

Cross-check aftermarket listings such as NGK BPR6ES (spark plug), Keihin HA-Y (carburetor), Stens 150-472 (recoil starter) against the OEM number and dimensions.

Best for annual tune-up

Bundle spark plug, air filter when servicing the Honda GX390 at the start of the season.

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 GX340? Parts may interchange with GX340, but verify the serial range, OEM number, and physical part details before ordering.

Should I buy OEM or aftermarket parts for the Honda GX390? 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 GX390? 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

OEM98079-56846Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Dimensions: 0.7mm gap

Brand	Part #
NGK	BPR6ES	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.
Champion	RC12YC	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-ZE3-505Confidence: Low · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Also fits GX340; different filter than GX160/GX200

Brand	Part #
No aftermarket listing is published for this part yet. Use the OEM reference and verify with a dealer or service manual before ordering.

Carburetor

OEM16100-ZF6-V01Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Keihin HA-Y float-type carb; also fits GX340

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

Recoil Starter

OEM28400-ZF6-003ZAConfidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Also fits GX340

Brand	Part #
Stens	150-472	Best overallAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Ignition Coil

OEM30500-ZF6-W31Confidence: Low · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Also fits GX340

Brand	Part #
No aftermarket listing is published for this part yet. Use the OEM reference and verify with a dealer or service manual before ordering.