Owner’s manual
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How to find Craftsman model number?
For Craftsman walk-behind mower model 917388851, the model and serial numbers are on a decal on the rear of the mower housing (deck). We recommend writing both down exactly as shown before ordering parts or checking specifications in the 917388851 owner’s manual.
Where to look on this Craftsman mower
Check these spots in order:
- Rear of the mower deck/housing (most common on this model)
- Near the rear discharge door area (still on the deck)
- On the handle support area close to the deck (less common)
What to record (and why)
Write down both numbers; they serve different purposes.
| Item | What it’s used for | Example format |
|---|---|---|
| Model number | Matching diagrams and compatible parts | 917.388851 |
| Serial number | Identifying production run details | Varies |
Tips to avoid mix-ups when ordering parts
- Copy the model number exactly, including dots or dashes if shown on the decal
- If the decal is dirty, wipe it gently so all digits are readable
- Use the model number first; then confirm the part fits your exact configuration
- If you’re replacing a wear item, match by model number and part description
Why it matters
Craftsman model numbers can look similar across different walk-behind mowers; using the exact model number helps ensure the blade, blade adapter, wheels, and control cable you choose are the correct fit.
Last updated: January 2026
How long can gas sit in a gas can for a lawn mower?
For the Craftsman 917388851 walk-behind mower, we recommend using gasoline within 30 days unless you treat it with a quality fuel stabilizer; untreated fuel can go stale quickly and cause hard starting. For longer storage, follow the fuel-system storage steps in the Craftsman 917388851 owner’s manual.
Recommended storage times (practical rule)
- Up to 30 days: Fresh, clean regular unleaded gas is typically fine.
- 30 days to 6 months: Use a fuel stabilizer and keep the can tightly sealed.
- 6 to 8 months: Stabilized fuel can often still be usable, but performance risk increases.
- Over 8 months: Plan to replace it with fresh fuel for best reliability.
Best practices for storing gas for your mower
- Store fuel in an approved gas can with a tight cap.
- Keep the can cool, dry, and out of direct sun.
- Buy only what you can use in a month during mowing season.
- If you use ethanol-blended fuel, be extra careful about storage time because it can attract moisture.
- Label the can with the purchase date so you know its age.
If the mower has been sitting (30 days or more)
The 917388851 manual calls out that to avoid engine problems during longer storage, you should either empty the fuel system or use stabilizer.
| Situation | What we recommend | Why |
|---|---|---|
| Storing fuel in a can | Stabilizer + sealed storage | Slows oxidation and varnish formation |
| Mower stored 30+ days | Run engine until fuel system is empty (or stabilize and run briefly) | Helps prevent carburetor gumming |
| Old fuel suspected | Drain and refill with fresh gas | Reduces no-start and surging issues |
Why it matters
Stale gasoline can leave varnish deposits in the carburetor and fuel passages, leading to hard starting, rough running, or a mower that will not stay running.
Last updated: January 2026
Should I use 87 or 91 gas for lawn mower?
For the Craftsman lawn mower model 917388851, use fresh, clean regular unleaded gasoline with a minimum of 87 octane. Using 91 octane will not improve performance on this mower; the correct fuel choice is about freshness and proper storage, not higher octane.
What the model 917388851 manual specifies
Our guidance for this exact mower comes from the fuel instructions in the 917388851 owner's manual. It calls for:
- Regular unleaded gasoline
- Minimum 87 octane
- No oil mixed into the gasoline
- Buying only what you can use within about 30 days (to keep fuel fresh)
87 vs 91 octane: what to choose
Octane is mainly about preventing knock in high-compression engines. Most walk-behind mower engines, including this Craftsman model, are designed to run correctly on regular fuel.
- Choose 87 octane for normal mowing and everyday use
- Choose 91 only if it is the only fresh fuel available; it is not a performance upgrade
- Avoid stale fuel (old gas is a much bigger problem than octane rating)
- Avoid overfilling; fill only to the bottom of the filler neck
Fuel tips that prevent hard starting and rough running
If you are troubleshooting starting or running issues, fuel quality and storage habits matter more than octane.
- Use fresh gas from a clean, approved container
- Wipe up spills and keep fuel off the mower tires and painted surfaces
- If the mower will sit 30 days or longer, run the engine until the tank and carburetor are empty (or use a stabilizer)
- Alcohol-blended fuels can attract moisture during storage; manage storage carefully
Quick comparison
| Fuel choice | OK for 917388851? | When it makes sense |
|---|---|---|
| 87 octane (regular) | Yes | Best everyday choice |
| 91 octane (premium) | Yes | Only if it is fresh and already on hand |
| Old/stale gas | No | Drain and replace |
Why it matters
Using the correct fuel for the Craftsman 917388851 helps prevent carburetor varnish, hard starting, surging, and poor power. In real-world mower problems, freshness and storage usually matter far more than premium octane.
Last updated: January 2026
