Chainsaw

Stihl MS 391

2-Stroke

The Stihl MS 391 is a 64.1cc 2-stroke Farm Boss chainsaw bridging Stihl's agricultural line and full professional class. It accepts 18" to 20" guide bars and targets ranchers and loggers who regularly fell large trees and process hardwood. The MS 391 runs a Walbro carburetor with professional anti-vibration. At this displacement, bar and chain condition directly affect engine longevity — a dull chain strains the fuel and ignition systems under load. Fuel system service (filter, primer bulb, lines) and annual carburetor inspection are the primary maintenance requirements.

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: Chainsaw · 2-Stroke
Covered Parts: Spark Plug, Air Filter, Fuel Filter, Carburetor, Recoil Starter, Ignition Coil, Primer Bulb, Fuel Line Kit, Chain, Guide Bar
OEM References: 0000 400 7000, 1140 140 4401, 0000 350 3518, 1140 120 0617, 1128 080 2106, 1128 400 1300, 4238 350 6201, 1140 358 7706
Model Family: MS 391
Last Reviewed: 2026-05-20
Data Confidence: Aftermarket-confirmed
Sources Consulted: OEM part references, Aftermarket catalog cross-references, Retailer fitment listings

Quick Fitment

Part Type	OEM / Spec	Common Option	Confidence
Spark Plug	0000 400 7000	NGK BPMR7A	Medium · 2026-05-20
Air Filter	1140 140 4401	Stens 605-644	Medium · 2026-05-20
Fuel Filter	0000 350 3518	OEM 0000 350 3518	Low · 2026-05-20
Carburetor	1140 120 0617	Zama C1Q-S279	Medium · 2026-05-20
Primer Bulb	4238 350 6201	Zama BG-00-4	Medium · 2026-05-20
Recoil Starter	1128 080 2106	Stens 150-644	Medium · 2026-05-20
Ignition Coil	1128 400 1300	OEM 1128 400 1300	Low · 2026-05-20
Fuel Line Kit	1140 358 7706	Stens 115-128	Medium · 2026-05-20

Tune-Up Kit

Common service bundle: spark plug, air filter, fuel filter, carburetor, primer bulb, fuel line kit.

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 Stihl MS 391, 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.
Assuming all fuel line kits use the same diameter and routing.
Installing the correct plug number with the wrong gap.
Matching bar length but missing pitch, gauge, or drive-link count.

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

Primer will not fill

Primer bulb, fuel line routing, in-tank filter

Cuts slowly

Chain pitch/gauge, bar wear, drive links

Replacement Options

Best OEM equivalent

Start with OEM references 0000 400 7000, 1140 140 4401, 0000 350 3518, 1140 120 0617 and match the removed part before choosing a listing.

Common aftermarket option

Cross-check aftermarket listings such as NGK BPMR7A (spark plug), Stens 605-644 (air filter), Zama C1Q-S279 (carburetor) against the OEM number and dimensions.

Best for annual tune-up

Bundle spark plug, air filter, fuel filter when servicing the Stihl MS 391 at the start of the season.

Best if replacing fuel system

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

Best chain/bar combo

Match chain specs together, especially pitch, gauge, drive links, and bar mount details.

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 other Stihl models? Use this page for the exact Stihl MS 391 unless a manual, dealer listing, or removed part confirms another model.

Should I buy OEM or aftermarket parts for the Stihl MS 391? 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 MS 391? 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.

What chain details matter besides bar length? Match pitch, gauge, and drive-link count against the bar stamp, old chain, and drive sprocket. Bar length alone is not enough.

Spark Plug

OEM0000 400 7000Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Dimensions: 0.5mm gap

Brand	Part #
NGK	BPMR7A	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.
Champion	RCJ6Y	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Air Filter

OEM1140 140 4401Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Fleece filter; fits MS311, MS362, MS391

Brand	Part #
Stens	605-644	Best for annual tune-upAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Fuel Filter

OEM0000 350 3518Confidence: Low · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Orange in-tank pickup body fuel filter

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

OEM1140 120 0617Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Zama C1Q-S279

Brand	Part #
Zama	C1Q-S279	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Recoil Starter

OEM1128 080 2106Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Also fits MS 311

Brand	Part #
Stens	150-644	Best overallAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Ignition Coil

OEM1128 400 1300Confidence: Low · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Also fits MS 311

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.

Primer Bulb

OEM4238 350 6201Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Newer units (SN# 287332321+) use 0000 350 6202

Brand	Part #
Zama	BG-00-4	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.
Hipa	G002-H	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Fuel Line Kit

OEM1140 358 7706Confidence: Medium · Source: Aftermarket catalog

Reviewed: 2026-05-20
Variant notes: Includes fuel pickup line and return line; fits MS311, MS362, MS391

Brand	Part #
Stens	115-128	Best if replacing fuel systemAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Chain

OEMSpec-based fitmentConfidence: Low · Source: Inferred

Reviewed: 2026-05-20
Dimensions: 20", 3/8" pitch, .050" gauge, 72 drive links
Variant notes: Stock bar length; verify drive link count matches your bar

Brand	Part #
Oregon	72LPX072G	Best chain/bar comboAmazonAffiliate link Some links may be affiliate links. Match the OEM number, dimensions, and model variant before buying.

Guide Bar