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If your EXI 625 lawn mower won’t start, the most common causes are stale or contaminated fuel, a fouled or worn spark plug, a clogged air filter, or a safety bail or key switch that isn’t engaged. Work through those four checks in order before assuming a bigger problem. Most no-start complaints are fixed with fuel, spark and air.
Why an EXI 625 Lawn Mower Won’t Start
Small engines need three things at the same time: fuel reaching the carburetor, a spark at the right moment, and enough clean air mixed in. Remove any one of those and the engine cranks but never catches. The EXI 625 is a small engine mower, so the same basic failure points apply to most walk-behind models in this class. For a broader overview of symptoms across mower types, see Lawn Mower Won’t Start: Common Causes.
Shopping for one? See our guide: 10 Best Remote Controlled Lawn Mower Options for Every Yard (2026).
Owners often report that the problem appeared after the mower sat for a few weeks. Gasoline begins to break down within about 30 days, and ethanol-blended fuel can separate and leave varnish in the carburetor jets. That varnish restricts flow, so the engine may sputter, fire briefly and die, or refuse to fire at all.
Fuel Problems: The Most Common Culprit
Stale fuel is the first thing to rule out. If the mower was last run in the fall, or the gas has been sitting in a can for more than a month, drain it and refill with fresh gasoline. Most manufacturers recommend using gasoline rated 87 octane or higher and avoiding fuel blends above 10 percent ethanol. Check your owner’s manual for the exact specification.
Next, check whether fuel is reaching the engine at all. Look at the fuel line between the tank and carburetor. If it is cracked, hardened or pinched, replace it. A fuel shutoff valve left in the closed position will also prevent starting, so confirm it is open.
Spark Plug and Ignition
A spark plug that is fouled with carbon, oil or moisture may produce a weak spark or none. Remove the plug with a spark plug socket, inspect the tip, and compare it against the gap specified in your manual. Typical small engine gaps fall in the range of about 0.030 inch, but confirm the number for your model before adjusting.
Ground the plug wire to bare metal and pull the starter cord or turn the key while watching for a blue, consistent spark. A weak or absent spark means a new plug is needed. Keep the replacement plug specified by the manufacturer to avoid heat-range problems.
Air Filter and Carburetor
A clogged air filter starves the engine of air, making it hard to start and prone to running rich. Remove the cover and inspect the filter. Paper filters should be replaced when they are dirty. Foam filters can be washed in warm soapy water, squeezed dry, and lightly oiled with engine oil before reinstalling.
If fuel is fresh, the spark is strong and the filter is clean, the carburetor is the likely cause. Varnish inside the jets is common after storage. A carburetor cleaning kit or a professional service may be needed. Avoid forcing the throttle or choke, which can flood the engine further.
Safety Switches and Controls
Modern mowers include safety systems that prevent starting unless certain conditions are met. Check that the operator presence bail is held against the handle when pulling the cord, that the choke and throttle are set correctly for a cold or warm start, and that the blade engagement control is in the disengaged position. A worn or misadjusted bail cable can also cause this problem, so inspect it for stretching or fraying.
Practical Steps to Get Your EXI 625 Running
- Confirm the fuel shutoff valve is open and the tank has fresh gasoline.
- Set the choke for a cold start and the throttle to fast.
- Hold the operator presence bail against the handle and pull the starter cord firmly several times.
- If it fires but dies, move the choke to half or off as the engine warms.
- Remove and inspect the spark plug. Clean or replace it as needed.
- Check and clean or replace the air filter.
- If the mower still won’t start, drain the old fuel, refill with fresh gas and try again.
- If none of these steps work, have a qualified small engine technician inspect the carburetor and ignition system.
For a seasonal angle, especially if the mower sat all winter, see How to Fix a Lawn Mower That Won’t Start After Winter. Owners of other mower types may find Why a Lawn Mower Engine Stalls While Mowing and How to Fix It useful if the engine starts but runs poorly.
What we’d use
A fresh spark plug matched to the manufacturer’s specification is the single most useful part to keep on hand for this type of engine.
Fuel stabilizer helps keep gasoline from breaking down during storage and reduces the chance of carburetor varnish.
A small engine carburetor cleaner spray can clear light varnish from jets without full disassembly.
Related questions
How long can gas sit in an EXI 625 before it goes bad?
Gasoline can begin to degrade within about 30 days, especially ethanol blends. Using a stabilizer or running the engine dry before long storage helps.
Should I use starting fluid on my EXI 625?
Starting fluid can help diagnose a fuel problem, but repeated use may damage the engine. Use it sparingly and fix the underlying cause.
Why does my mower start and then die?
This usually points to a restricted fuel flow, a clogged air filter or a choke that is still engaged. Adjust the choke as the engine warms and check the filter.
How often should I replace the spark plug?
Many owners replace the plug once a season or every 100 hours of use, but follow the schedule in your owner’s manual.
