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Should I use 87 or 91 gas for lawn mower?
For the Craftsman 987889010 gas walk-behind mower, we recommend using regular 87-octane gasoline; higher octane (like 91) does not add power or protection in a mower engine and usually just costs more. The bigger priority is using fresh, clean fuel and the right oil level.
What to use (and what to avoid)
- Use 87 octane (regular unleaded) for normal mowing.
- Use fresh fuel; old gas is a top cause of hard starting and rough running.
- Avoid fuel that has been sitting in the can or tank for weeks or months.
- If you have a choice, ethanol-free fuel helps reduce storage and carburetor issues.
- If you must use E10 (10% ethanol), use a fuel stabilizer when the mower will sit.
Quick comparison: 87 vs 91 in a mower
| Fuel choice | What it changes | When it makes sense |
|---|---|---|
| 87 octane | Normal performance for small engines | Everyday mowing |
| 91 octane | Typically no performance gain | Only if it is the freshest fuel available |
Why it matters
Most walk-behind mower engines are designed to run correctly on regular fuel. Problems that feel like “bad gas” are usually caused by stale fuel, water contamination, or varnish in the carburetor jets, not octane rating.
If your mower is hard to start or runs rough
- Drain old fuel from the tank and refill with fresh 87 octane.
- Check the oil level; low oil can cause poor running and engine damage.
- Inspect the spark plug condition and gap.
- If the mower still will not start, follow a step-by-step ignition and fuel check in lawn mower wont start troubleshooting video fuel ignition and compression.
- If the recoil rope is difficult to pull, use lawn mower pull cord stuck to diagnose possible blade or engine binding.
Last updated: January 2026
What model number is the Craftsman 987889010?
The model number for this Craftsman walk-behind mower is 987889010. You’ll use 987889010 to look up the correct Craftsman parts diagrams and to match replacement items like belts, blades, and hardware to your exact mower.
Where to find the model number on the mower
Most walk-behind mowers list the model number on a product ID label. Check these common spots:
- Rear of the mower deck (near the discharge chute)
- Top of the deck near the engine mounting area
- Behind the engine, on the deck surface
- On the handle support or rear frame area
Why the exact model number matters
Craftsman mowers can look similar but use different parts by year and build. Using 987889010 helps ensure you get the right fit for items like:
- Drive belts and blade drive belts
- Blade and spindle components
- Handle and control hardware
- Wheels, height adjusters, and fasteners
Quick check: model number vs. other numbers you may see
| What you see on the mower | What it means | Use it for parts lookup? |
|---|---|---|
| 987889010 | Sears PartsDirect model number | Yes |
| Engine model/type/code | Engine identification | Sometimes (engine parts only) |
| Deck size (example: 21-in) | Cutting width | No (not specific enough) |
Helpful next step if you’re servicing the mower
If you’re doing routine maintenance, our DIY guide on how to tune up a lawn mower video walks through common tune-up steps (spark plug, air filter, oil, and basic checks) that apply to most gas walk-behind mowers.
Why it matters
Matching parts to the correct model number prevents returns and helps your mower run safely and cut evenly.
Last updated: January 2026
What year is my Craftsman mower serial number lookup?
For a Craftsman walk-behind mower like model 987889010, the year is usually encoded in the serial number or date code, but the exact format depends on who built the mower and where the label is located. We use the model and the full serial/date code together to identify the correct production year.
Where to find the serial number/date code
Check these common label locations on a Craftsman walk-behind mower:
- Rear of the mower deck (near the discharge chute)
- Top of the deck near the engine mounting area
- Handle bracket area (left or right side)
- Under the engine shroud (less common)
- On a sticker or stamped plate with the model number
How to decode the “MMDDYY” style date code (common format)
Some Craftsman and MTD-built products use a 6-digit date code that reads like MMDDYY:
- MM = month
- DD = day
- YY = year
Example
| Code | Month | Day | Year |
|---|---|---|---|
| 072811 | 07 | 28 | 2011 |
Other serial number formats we see (and what they mean)
Not every Craftsman mower uses MMDDYY. Here are other common patterns:
- 10+ characters with letters and numbers: often a manufacturer serial (year may not be obvious)
- Two-digit year embedded near the beginning or end: sometimes YY appears as part of a longer string
- Engine serial number vs. mower serial number: the engine tag (Briggs and Stratton, Honda, etc.) is different from the mower’s model/serial tag
Why it matters
Getting the correct year helps us match the right diagrams and parts for your Craftsman 987889010 (for example, belts, deck hardware, and drive components). If you are servicing the drive system, parts like the troy-bilt lawn mower ground drive belt 1770334 are selected by exact model and configuration, not just by appearance.
Quick checklist before ordering parts
- Confirm the mower model number is 987889010
- Write down the entire serial number/date code (include letters)
- Use the mower tag, not the engine tag, for chassis and deck parts
- Compare your deck and drive layout to the parts diagram before buying
Last updated: January 2026
