Generator Won't Start Checklist
The spark plug is the cheapest part on your mower and the most informative: a few dollars, ten minutes to change, and the old plug comes out carrying a written report on how the engine has been running. Our technicians replace plugs on nearly every service visit and read hundreds a season. This guide covers the signs a plug has gone bad, the change itself done properly (gapping and torque are where DIY goes wrong), and the color chart that turns your old plug into a diagnosis.
Safety
Keep the generator outdoors and follow the manufacturer's operating and electrical safety guidance before any inspection.
- Harder starting, more pulls or longer cranking than the engine used to need.
- Misfiring and rough running, stumbles and skips, especially under load in thick grass.
- Noticeably higher fuel use, because weak incomplete combustion wastes gas.
- Engine cutting out momentarily, or refusing to start at all when the plug finally fails, the symptom tree covered in our cranks but will not start guide.
- Visible damage on inspection: a rounded, eroded center electrode, cracked porcelain, or heavy deposits bridging the gap.
Because the plug costs so little, the threshold for replacement is low: when in doubt, swap it, and keep the old one in the garage as a get home spare.
Fuel
Old fuel and deposits can contribute to no-start problems, so fuel condition is part of a practical inspection.
Ignition
Cool engine, wire off
Spark plug condition can affect starting and operation and should be evaluated without bypassing safety controls.
Operate outdoors
Never run a portable generator in an enclosed or partly enclosed space.
Do not bypass controls
Keep electrical and engine safety controls intact during troubleshooting.
Use qualified service
Voltage and internal electrical checks should be handled with appropriate expertise.
Operate outdoors
Never run a portable generator in an enclosed or partly enclosed space.
Do not bypass controls
Keep electrical and engine safety controls intact during troubleshooting.
Use qualified service
Voltage and internal electrical checks should be handled with appropriate expertise.
Voltage and service checks
Generator service can include no-start repair, carburetor service, voltage checks, and routine maintenance after diagnosis.
| Plug Appearance | What It Means | What to Do |
|---|---|---|
| Light tan or gray, dry | Healthy engine, correct mixture | Nothing, this is the goal |
| Black, dry and sooty | Running rich: too much fuel or too little air | Service the air filter, check the choke, suspect the carburetor |
| Black, wet and oily | Oil entering the cylinder: overfill, tipping, or wear | Check oil level, review how the mower was tilted, persistent oil fouling needs a technician |
| Wet with gasoline | Flooded engine or no spark reaching the plug | Dry it and follow our flooded engine guide |
| White, blistered or glazed | Running lean and hot: restricted fuel or an air leak | Suspect a varnished carburetor or intake leak, see the surging guide |
| Eroded electrode, wide gap | Simple old age | Replace and note the interval |
A black sooty plug is the one owners ask about most, and the message is rich running: the engine is getting more fuel than its air can burn. New plugs cure the symptom for a while, but the fix is on the air and fuel side, a clean filter and often a carburetor that needs cleaning.
Service
If the generator still will not start, request an in-person inspection before repair work or electrical testing is attempted.
Need an in-person inspection?
Share the equipment type and symptoms so the service scope and availability can be confirmed.