Does your lawn mower start and run fine—once you finally get it going—but sometimes it’s stubborn and won’t start at all? Maybe it cranks, coughs, or sputters, then eventually runs normally, or maybe it runs great after you get it started but takes a lot of effort to fire up. This is a frustrating but common problem with both gas and electric mowers. Here’s a simple troubleshooting guide to get your mower starting reliably, every time.
Quick Picks: Most Common Reasons a Lawn Mower Runs but Won’t Start Easily
- Old or Bad Gas: Fuel that’s more than a month old can cause hard starting—even if the mower runs fine after starting.
- Dirty or Clogged Carburetor: Gum and varnish block jets, making starting tough but not always affecting running at speed.
- Weak or Fouled Spark Plug: A spark plug that’s worn, dirty, or gapped wrong can make starting difficult but allow running once warmed up.
- Dirty Air Filter: Choked airflow can make the engine hard to start but let it run once it’s warmed up.
- Choke or Primer Issue: If the choke or primer isn’t working, the engine may not get enough fuel for an easy cold start.
- Low Compression: Worn piston rings or a leaking head gasket make starting difficult but don’t always stop the engine from running after you get it going.
- Weak Battery (Electric Start): For electric start mowers, a weak battery may crank the engine too slowly for easy starting.
Buyer’s Guide: What You’ll Need to Troubleshoot
- Fresh gasoline
- Spark plug wrench
- New spark plug and air filter
- Carburetor cleaner
- Battery charger (for electric start mowers)
- Work gloves
Step-by-Step: How to Fix a Mower That Runs but Won’t Start Easily
1. Replace Old Gas with Fresh Fuel
- Drain the tank if fuel is more than 30 days old.
- Refill with fresh, ethanol-free gasoline for best results.
2. Clean or Replace the Air Filter
- Remove the air filter and check for dirt, dust, or oil. Clean or replace as needed.
3. Check, Clean, or Replace the Spark Plug
- Remove the spark plug and inspect for fouling, wear, or a too-wide gap.
- Clean with a wire brush or replace with a new, properly gapped plug.
4. Clean the Carburetor and Jets
- Spray carburetor cleaner into the carb throat and around the choke plate.
- If problems persist, remove and clean the carburetor thoroughly.
5. Check Choke and Primer Operation
- Verify the choke closes fully when starting and opens as the engine warms.
- If the primer bulb is cracked or leaks air, replace it.
6. Test Battery and Charging System (Electric Start Models)
- Charge the battery fully. If the engine cranks slowly, replace the battery.
7. Check for Low Compression (If All Else Fails)
- If the engine is very hard to start cold but runs well warm, you may have worn rings or a bad head gasket. This repair is best left to a small engine shop.
Comparison Table: Hard-Starting Mower Causes & Solutions
| Problem | Solution | Difficulty | Parts Needed |
|---|---|---|---|
| Old/Bad Gas | Drain & refill with fresh fuel | Easy | Gasoline |
| Dirty Carburetor | Clean carburetor | Easy-Medium | Carb cleaner |
| Weak/Fouled Spark Plug | Clean or replace spark plug | Easy | Spark plug |
| Dirty Air Filter | Clean or replace air filter | Easy | Air filter |
| Choke/Primer Fault | Fix/replace choke or primer | Easy | Choke/primer |
| Low Compression | Repair rings/head gasket | Hard | Rings/gasket |
| Weak Battery | Charge or replace battery | Easy | Battery |
Frequently Asked Questions
Why does my mower run fine after it finally starts?
Starting requires a rich fuel mixture and strong spark—small problems with gas, spark, or air are more noticeable during starting than running.
How can I make my mower start easier?
Keep fuel fresh, change the plug and air filter every season, and use carb cleaner regularly.
Is it expensive to fix a hard-starting mower?
Most hard-starting problems are inexpensive DIY fixes. Major engine repairs (low compression) can be costly and are best left to a shop.
Conclusion
If your mower runs well but is hard to start, check gas, spark plug, filter, carburetor, and choke first. Most fixes are easy and will get your mower starting on the first try all season long!