John Deere Mower Won't Start? Causes & How to Fix It

When a John Deere mower won't start, the culprit is almost always fuel-related — stale gas that has gummed up the carburetor over the off-season, a fouled spark plug, or a clogged air filter. All three are cheap, DIY-friendly fixes.

Disconnect the spark plug boot before working near the blade or removing the plug.

Get your exact fix

Enter your model for an instant diagnosis tuned to your exact John Deere — ranked causes, the right parts, and a step-by-step repair guide. John Deere lawn tractors pair a Briggs/Kawasaki engine with a hydrostatic or gear drive.

Most likely causes

01Stale fuel / gummed carburetor
55%
Gas older than ~30 days varnishes the carb jets — the #1 no-start cause after storage.
How to check: Drain a little fuel into a clear cup — sour/varnishy smell or gas older than a month means it's stale. Then pull the carb bowl: green/white gum or a crusty main jet confirms it.
Reference: Engine service manual — fuel & carburetor
02Fouled or worn spark plug
22%
A carbon-fouled or wet plug won't spark; a $4 plug often brings it right back.
How to check: Pull the plug — a wet, black, or oil-caked tip is fouled. Ground the threads to the engine and pull the cord: no blue spark at the gap confirms a dead plug.
Reference: Engine service manual — ignition & spark
03Clogged air filter
13%
A choked filter starves the engine of air so it won't fire or catches then dies.
How to check: Hold the filter up to a light — little or no light through (or caked with dust/oil) means it's choking the engine. If it fires briefly with the filter off, that was it.
Reference: Engine service manual — air intake & filter
04No fuel flow (closed valve / clogged line)
10%
A shut fuel valve, kinked line, or blocked cap vent stops gas reaching the carb.
How to check: With the valve open and gas in the tank, pull the fuel line off the carb inlet into a cup — little or no flow means a clogged line/filter or a non-venting cap.
Reference: Engine service manual — fuel & carburetor

Parts you may need

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How to fix it

7 steps

1
Rule out the easy stuff first
5 min
Confirm there's fresh gas in the tank, the fuel valve is open, and the choke/primer is set correctly. Then pull the spark plug and look at the tip — wet or black means fouled. This 5-minute check solves a surprising number of no-starts before you touch the carburetor.

The rest of the repair

02Drain old fuel and refill with fresh gas + stabilizer
03Clean or replace the spark plug and set the gap
04Remove and clean (or replace) the air filter
05Spray carburetor cleaner through the carb and let it soak
06Remove the carburetor bowl and clear the main jet
07Reassemble, prime, and test-start

The full guide adds torque specs, spark-plug gap, the exact carburetor teardown, and when to just replace the carb. Run the free diagnosis above to unlock it for your model.

Frequently asked

Why won't my John Deere mower start after winter?

Fuel left in the tank over winter breaks down and clogs the carburetor. Drain the old gas, add fresh fuel with stabilizer, and clean the carb — that fixes the large majority of post-winter no-starts.

My John Deere mower has spark and fuel but still won't start — now what?

Check the air filter and carburetor. If air and fuel are getting in and there's spark, a gummed main jet or a stuck float in the carburetor is the usual remaining cause.

How much does it cost to fix a John Deere mower that won't start?

Usually $10–$40 in DIY parts (plug, filter, carb cleaner or a carb kit). A shop typically charges $75–$150 for the same job.