Craftsman 917378840 gas walk-behind lawn mower Parts

For a Craftsman walk-behind mower like model 917378840, the model number is typically printed on a decal or tag on the mower deck (often near the rear wheel area) or on the rear housing. Use that exact number to match the correct parts list and diagrams in the 917378840 owner's manual.

Where to look on a walk-behind mower

Check these common locations with the mower on a flat surface and the engine off:

• Top of the mower deck near the rear discharge area
• Rear of the deck near the height adjuster hardware
• Side of the deck near a rear wheel
• Handle support bracket area (near where the handle bolts to the deck)
• Grass bag frame area (if equipped)

What the model number looks like

On this Craftsman mower, the manual identifies the model as 917.378840 (you may see it with or without the dot). When searching parts, enter it as 917378840.

You see on the tag/manual	Use for parts lookup
917.378840	917378840

Tips to make sure you have the right number

Model tags can be dirty or faded, so a quick cleanup helps.

• Wipe the tag with a damp rag; avoid harsh solvents that can remove printing
• Take a clear photo and zoom in to read small characters
• Write down the full model number before ordering parts
• Match the model number to the exploded-view diagrams in the manual

Why it matters

Craftsman walk-behind mowers often share similar frames and engines, but parts like the engine zone control cable, drive components, and wheel hardware can vary by model. Using the exact model number helps you get the correct fit the first time.

Last updated: February 2026

For the Craftsman 917378840 gas walk-behind lawn mower, we recommend using 87-octane unleaded regular gasoline. Using 89-octane will not improve performance in normal mowing, and the key is using clean, fresh fuel and the correct oil type listed in the owner's manual.

What the 917378840 manual specifies

The product specifications for this mower call for unleaded regular gasoline (capacity: 1.6 quarts). That aligns with using 87 octane at the pump for typical small-engine operation.

When 89 octane makes sense (and when it does not)

Higher octane is mainly about preventing knock in engines designed for it. Most walk-behind mower engines are designed to run correctly on regular fuel.

Use this quick guide:

• Use 87 octane for everyday mowing and storage cycles
• Use fresh fuel (old gas is a common no-start cause)
• Avoid mixing oil into the gas (this is a 4-cycle mower; oil goes in the crankcase)
• Keep fuel off tires and painted surfaces to prevent damage
• Store fuel properly and consider stabilizer for longer storage

Fuel and oil specs at a glance

Item	What to use	Notes
Gasoline	Unleaded regular (typically 87 octane)	Capacity: 1.6 quarts
Engine oil (above 32°F)	SAE 30	Use the correct fill amount
Engine oil (below 32°F)	SAE 5W-30	Helps cold-weather starting

Why it matters

Using the correct fuel helps prevent hard starting, rough running, and carburetor varnish. In small engines, fuel freshness and clean storage matter more than stepping up from 87 to 89 octane.

Last updated: February 2026

Common problems on the Craftsman 917378840 gas walk-behind lawn mower are no-start conditions (stale fuel, dirty air filter, spark plug or wire issues, control bar released), loss of power from heavy grass or deck buildup, and poor or uneven cutting from blade or wheel-height issues.

Most common symptoms and likely causes

• Won’t start: stale fuel, dirty air filter, water in fuel, spark plug issue, control bar not held to the handle
• Loss of power: heavy grass drag, cutting too much at once, dirty air filter, grass buildup under the deck
• Poor or uneven cut: worn or loose blade, uneven wheel heights, debris packed under the mower housing
• Hard to pull starter rope: blade obstruction or a blade adapter problem

Quick checks we recommend first

• Drain and refill with fresh gasoline if fuel is old
• Clean or replace the air filter
• Push the spark plug wire on firmly; replace the plug if fouled
• Hold the control bar against the handle while starting
• Disconnect the spark plug wire, then clean packed grass from under the deck

Troubleshooting by symptom

Symptom	Most likely causes	What to do next
Won’t start	Fuel, air filter, spark plug or wire, control bar released	Refresh fuel, service filter, check plug and wire, hold control bar
Loss of power	Heavy grass, deck buildup, dirty filter	Raise cut height, slow down, clean deck, service filter
Poor cut	Blade condition, wheel heights, deck buildup	Level wheels, clean deck, service blade and hardware

Parts that often relate to drive and cutting complaints

• Self-propel slips or won’t drive: check the lawn mower ground drive belt, 3/8 x 32-1/2-in 532175436
• Poor cut after blade service: inspect the lawn mower blade adapter 581547901

Why it matters

Most mower problems come from basic maintenance (fuel, airflow, deck cleaning) and a few wear items (belts, blade adapter). Fixing these early improves starting, power, and cut quality.

For the model-specific troubleshooting chart and maintenance schedule, use the owner's manual.

Last updated: February 2026

For the best value, we recommend choosing a self-propelled mower that matches your yard size, terrain, and maintenance comfort level; if you already own the Craftsman 917378840, keeping it running well is often the best “for the money” option because routine tune-ups and a fresh drive belt restore performance for far less than replacing the mower. See the owner's manual for operating and maintenance guidance.

How to pick the best value self-propelled mower

Focus on the features that change real-world performance and ownership cost:

• Drive system: front-wheel drive for flatter yards, rear-wheel drive for hills and uneven terrain
• Deck size: most walk-behind mowers are 21 inches; wider decks reduce passes but add weight
• Cut options: bagging, side discharge, and mulching (mulching reduces bagging time)
• Speed control: single-speed is simpler; variable speed is more comfortable for mixed terrain
• Maintenance needs: gas mowers need seasonal fuel and tune-up attention; battery mowers reduce engine maintenance

If you already have a Craftsman 917378840, value usually means repairing it

This model is a 6.5 HP, 21-inch, power-propelled rotary mower. When it “won’t move” or self-propel feels weak, the most common value fix is restoring the drive system.

Common repair wins:

• Replace a worn or stretched ground drive belt
• Inspect the drive control lever and cable adjustment
• Check wheels for binding and debris buildup
• Confirm the operator presence control bar and drive control engage correctly

Quick parts comparison (common value repairs)

Symptom	Likely area	Example part on this model page
Mower won’t self-propel	Belt slipping/worn	Lawn mower ground drive belt, 3/8 x 32-1/2-in 532175436
Drive engagement feels inconsistent	Control linkage/cable	Control 532184588
Poor traction or wobble	Wheel wear/damage	Lawn mower wheel 532180552

Why it matters

“Best for the money” is usually the mower that delivers the cut quality you need with the lowest total cost over time. For many owners, a solid Craftsman gas walk-behind mower plus basic maintenance (clean deck, sharp blade, fresh fuel, and a healthy drive system) beats the cost of replacing the entire machine.

Last updated: February 2026