Gas Lawn Mower Won't Start
So, what's the problem with a gas lawn mower that won't start? The most likely reasons a gas mower won't start, is a dirty carburetor and bad gas, but other possible reasons include:
- Fuel valve off
- Choke not on
- Plug wet / faulty
- Plug wire off
- Air filter blocked
- Carburetor faulty
- Coil fault
- Bail lever / ignition fault
- Flywheel timing (Broken Shear-key)
- Sticking valves
- Low engine compression
I know what you're thinking. Yes, it's a long list but lets think positive, doing some basic checks will sometimes solve the problem or at least point us in the right direction.
The basics include: oil level check; fuel level check; fuel tap on; air filter check; plug wire on; choke applied; bail lever applied.
Lets take a look at the basics and rule out all the easy stuff first.
Air Filter Check
Plug Wire On
Bail Lever Applied
Fresh gas in the tank?
Plug wire on and secure?
All engines require the right amount of air, if the air filter is blocked, it can prevent starting.
Try starting without the air filter.
Bad Gas Causes Most Problems
Lets Dig A Little Deeper
Attempt to start your mower in the normal way.
There are two possible outcomes -
(1) Mower attempted to start or started - tells us we have a fueling fault, most likely a dirty carburetor, but first we will check the choke. Check out "Choke system".
(2) Mower made no attempt to start - then we've likely eliminated a fueling fault, and the fault will probably be a lack of spark. Check out "Ignition system check".
Testing The Choke
Remove the air filter, this allows us view the choke plate.
If you have a manual choke control, move throttle lever to full choke position to start a cold engine.
Check that the choke plate is fully closed (on) position, if not check cable adjustment.
Your mower may have auto choke. If so, when cold, the choke plate should be closed, as per picture. If not, move plate by hand to see if its stuck. If sticking, try WD40, if not replace thermostat.
Primer bulb can be checked by pressing the bulb and looking into the carburetor, you should see the gas being squirted in.
If you found no issues with your choke system, move on to "Gas Bowl Clean".
Where's the carburetor on a lawn mower? The carburetor on a lawn mower is located behind your air-filter cover, on the side of the engine. The air-filter cover is usually a square shaped black plastic cover. Typically the carburetor is on the opposite side to the muffler.
Lawn mower keeps flooding? A lawn mower engine that floods consistently has a failed carburetor float needle. The needle ca be replaced but often it makes more sense to replace the whole carburetor.