This is Why Your Zero Turn Mower is Sputtering: Solved!

Your zero turn isn’t running as it should. It’s bogging down and running sluggish. Many of the items that cause the mower to sputter can be prevented with routine maintenance.

I’ll go through a list of items that can be easily addressed along with those that may need an experienced small engine mechanic to repair.

A zero-turn mower will sputter when the fuel is old or contains water; the air filter is plugged; the fuel system is clogged due to a dirty carburetor or plugged fuel lines; a bad spark plug, a plugged mower deck, or a slow engine speed.

Check out the items listed below for a list of items that can cause a sputtering issue. These are simpler routine procedures most owners should be able to tackle. Make sure you follow safety precautions as outlined in your owner’s manual.

If you find these are not the cause of your engine problem or you don’t feel comfortable tackling the repair, take your mower to your local small engine mechanic for repair.  

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

6 Reasons Your Zero Turn Mower is Sputtering

Old Fuel in Your Zero Turn Mower

Using the right type of fuel and properly caring for that fuel is important when maintaining your zero-turn. Gas-powered mowers require unleaded gasoline with a minimum octane rating of 87 that contains no more than 10% ethanol.

Gasoline can begin to break down and become less effective as quickly as 30 days after purchase. Ethanol found in most gasoline will attract moisture. This moisture is corrosive to the fuel system.

The ethanol and moisture mix can leave behind a gummy residue that clogs the fuel system not allowing your mower to get sufficient fuel so it may begin sputtering. Read more about the right gas to use in your mower here.

Water in the fuel tank can also cause your zero-turn to sputter. Water separates from the gas and sinks to the bottom of your fuel tank. Water can get into the tank when the mower is left outside during a hard rain. The seal in your cap may not keep the water out.

If you find water in the tank, drain your fuel tank and fill it with fresh fuel. Add a fuel additive like Sea Foam to stabilize your fuel and reduce moisture. Read more about why I choose to use Sea Foam in every tank of fuel I use in my zero-turn mower.

Plugged Air Filter in Your Zero Turn Mower

Mowing your lawn stirs up a lot of dirt and debris that can plug your air filter. It’s important to regularly check your filter and clean it to ensure the mower is getting sufficient airflow.

When the air filter becomes plugged, the engine will begin to run sluggish and sputter. Not only will a plugged filter cause your mower to run like crap, it can also cause damage to your engine if not addressed.

I recommend installing a new filter annually and cleaning it several times throughout the mowing season. Find more information on air filters and how to clean them here.

Bad or Dirty Carburetor in Your Zero Turn Mower

Along with air, your zero turn needs fuel to be mixed with it to form a combustion. The carburetor regulates the gas-to-air mixture to keep your mower running.

When the air-to-fuel mixture is off and your engine is getting too much air or too much fuel, the engine will run rough.

Your carburetor could be dirty from running old fuel that clogs and gums up internal components preventing sufficient fuel flow. Before removing your carburetor to clean it, make sure you are getting fuel to the carburetor.

Then remove your air filter, spray carburetor cleaner into the air intake and start your mower. If your engine runs fine and then shuts off, there is a good chance your carburetor is dirty.

Follow these instructions to clean your zero-turn’s carburetor. Replace any damaged parts or replace your carburetor if it still doesn’t function properly after cleaning.

Bad Spark Plug in Your Zero Turn Mower

A dirty spark plug that fouls out will cause the engine to run rough and sputter. Check your spark plug condition by removing the spark plug wire by hand. Next, remove the spark plug with a spark plug wrench.

Clean or replace a spark plug where there is oil or carbon buildup. You can use brake cleaner or rubbing alcohol along with a wire brush to remove the buildup. When the tip is very dark, I recommend installing a new spark plug.

Make sure the plug is gapped to the manufacturer’s specification and that the spark plug wires are securely in place.

Engine Speed is Too Low in Your Zero Turn Mower

Always operate your mower at full throttle when you have your mower deck engaged. Your mower will bog down and sputter when it is not operating at a high engine speed.

If you are running your mower at full throttle and your engine isn’t giving you the power it once did, take your mower to your local small engine mechanic to have it checked out.

Plugged Mower Deck in Your Zero Turn Mower

Over time, your deck will become packed with grass clippings, dirt, and other debris. Mowing wet grass will plug your deck more quickly than mowing dry grass.

The engine will begin to bog down when it must work harder to turn the blades through a deck packed with debris. Having to turn dull mower blades further magnifies the problem.

Regularly scrape your zero-turn mower deck to keep it clean and free of debris. Check and sharpen your mower blades after every 25 hours of use. Read more about mower blade care and how to sharpen your blades here.

Always take additional safety precautions when working under your mower deck. Remove the ignition key and spark plug wires. Never reach under your deck until all moving parts have stopped. Protect your hands from the sharp edges of your blades.

Experiencing More Problems with Your Zero Turn Lawn Mower

There are many items that can impact the running efficiency of your zero-turn mower. If you checked all the items above, it may be time to take your lawn mower to a local mechanic for repair.

You can also check out my handy guides on common zero-turn problems and other issues that can result in the same sputtering symptom.

Common Zero Turn Problems: How to Fix Them

10 Reasons Your Zero Turn Won’t Turn Over

Your Zero Turn Mower Quits When Hot

Your Zero Turn Loses Power