Owner’s manual
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Should I use 87 or 91 gas for lawn mower?
For the Craftsman 917378781 gas walk-behind lawn mower, 87 octane (regular unleaded) is the right choice for normal mowing. Higher octane (like 91) does not add power in this type of small engine; the bigger priority is using fresh fuel and avoiding fuel that causes storage-related fuel system damage.
What fuel to use (and what to avoid)
- Use fresh, clean regular unleaded gasoline (87 octane).
- Avoid old or stale gas; it is a common no-start cause.
- Be careful with alcohol-blended fuels (ethanol/methanol blends) because they can attract moisture and separate during storage, creating acids that can damage the fuel system.
- If the mower will sit 30 days or longer, plan to empty the fuel system before storage.
- Do not put engine or carburetor cleaner products into the fuel tank.
Best practice for storage (30 days or longer)
Our recommended routine for the 917378781 is:
- Drain the gas tank.
- Start the engine and let it run until the fuel lines and carburetor are empty.
- Refill with fresh fuel next season.
For the full storage and fuel guidance, follow the steps in the Craftsman 917378781 owner's manual.
Quick comparison: 87 vs 91 for this mower
| Fuel choice | Works for mowing? | Best use case | What matters most |
|---|---|---|---|
| 87 octane (regular) | Yes | Everyday mowing | Freshness and clean fuel system |
| 91 octane (premium) | Yes | Not needed for performance | Does not fix stale fuel or moisture issues |
Why it matters
Most “fuel problems” on walk-behind mowers come from stale fuel, water contamination, or storage issues, not octane rating. Using 87 octane and managing storage correctly helps protect the carburetor and fuel lines and improves starting reliability.
Last updated: January 2026
What model number is the Craftsman 917378781?
The model number for this Craftsman gas walk-behind lawn mower is 917.378781 (often written without the dot as 917378781). You’ll see it printed in the parts list and diagrams for the mower, and it’s the number to use when ordering parts for the correct fit.
Where to confirm the model number
We recommend checking the model identification on the mower and matching it to the documentation:
- Look for the model label on the mower deck, rear housing, or handle support area
- Match the number to the parts diagrams in the Craftsman 917378781 owner's manual
- Use the full model number when searching parts (including the dot if shown)
- If the label is worn, use the manual’s illustrated parts breakdown to confirm assemblies
Why you might see it written two ways
Both formats refer to the same mower model.
| How it appears | What it means | When you’ll see it |
|---|---|---|
| 917.378781 | Same model number with a dot | Manuals, parts lists, decals |
| 917378781 | Same model number without punctuation | Online search, ordering, databases |
Why it matters
Using the exact model number helps us match the correct Craftsman parts and hardware for your mower’s specific build, including drive system components like the gear case and wheel assemblies.
If you’re ordering drive-related parts, match the part description and ID carefully, such as the input shaft 532183502 shown in the gear case assembly breakdown.
Last updated: January 2026
Where can I find the Craftsman mower model number?
On your Craftsman gas walk-behind lawn mower, the model number is printed on the mower’s ID label, and for this unit it should read 917.378781 (often shown without the dot as 917378781). Use that mower model number, not the engine numbers, when ordering non-engine parts.
Where to look on the mower
Check these common ID-label locations on Craftsman walk-behind mowers:
- Rear of the mower deck, near the bagger door or discharge area
- Top of the deck near the engine mounting area
- Side of the deck near a rear wheel height adjuster
- On the handle support/bracket area near the lower handle bolts
If the label is dirty or faded, wipe it with a damp rag first; grass dust and oil film can hide the print.
What the label should show
Most labels include a few different identifiers. Use the mower model number for parts lookups.
| Label item | What it’s used for | Example for this mower |
|---|---|---|
| Mower model number | Ordering chassis and drive parts | 917.378781 (917378781) |
| Product number | Retail/packaging reference | Varies |
| Engine model/type/code | Engine-specific service parts | Varies |
Why it matters
Craftsman walk-behind mowers often share similar decks and handles, but the drive system, control cable routing, and wheel hardware can differ by model. Using 917378781 helps ensure you get the correct drive parts, hardware, and assemblies listed for your exact mower.
Tip if you’re matching a part from the diagram
If you’re using the parts diagrams in the manual to confirm what you have, the exploded views and key numbers for model 917.378781 are shown in the 917378781 owner’s manual.
Last updated: January 2026
