10 Common Lawn Mower Breakdowns You Can Fix Yourself

Your mower stopped in the middle of the job? Engine stalling or grass cutting unevenly? Most problems with lawn equipment don’t need expensive service center repairs. Experience shows that mower owners waste money on simple malfunctions that can actually be fixed in 20-30 minutes with a basic tool set.

Let’s look at typical breakdowns that users of gas and electric models face, and show how to fix them without special skills.

1. Engine Won’t Start

The most common complaint from gas mower owners – the engine cranks but won’t fire up. First thing to check – fuel. Gas that’s been sitting in the tank for over a month loses its properties. Octane rating drops, resins form. Husqvarna and Honda recommend draining fuel before long-term storage, but few people actually do it.

If the gas is fresh, check the spark plug. Unscrew it with a spark plug wrench and look at the electrode. Black buildup or an oily film means trouble. You can clean the plug with a wire brush or just replace it. A new one costs $2-5 depending on the model.

Another thing – air filter. A clogged filter doesn’t let oxygen through, making the mixture too rich. The engine floods and won’t start. You can wash the filter with soapy water (if it’s paper – just tap it lightly) or buy a new one.

2. Engine Dies Under Load

Mower starts but dies as soon as it hits thick grass? The problem often lies in the carburetor. Jets get clogged with dirty gas or oxidation products. In models like Briggs & Stratton, the carburetor is located on the side of the engine with easy access.

For cleaning, you need a can of carburetor cleaner spray. Remove the air filter, start the engine, and spray the cleaner into the carburetor throat in short bursts. The engine might smoke – that’s normal, the buildup is burning off. Repeat the procedure 2-3 times.

If that doesn’t help, the carburetor needs to come off for disassembly. Blow out the jets with compressed air or thin wire. Main thing – don’t enlarge the hole, or fuel consumption will increase.

3. Dull Blades

Mower doesn’t cut grass but tears it? Grass tips turn whitish, lawn looks sick? This means the blades have dulled. Blade sharpness is critical for quality cutting.

Replacing or sharpening blades is straightforward. Tip the mower on its side (always on the side that keeps the spark plug facing upwards to prevent oil/fuel leaks into the air filter or cylinder), block the blade with a wooden block, and unscrew the center bolt. Usually it’s a 14-17mm bolt, tightened pretty firm.

The removed blade gets sharpened with a grinder or file at about a 30-degree angle. Important to remove metal evenly from both ends to maintain balance. An unbalanced blade creates vibration that destroys shaft bearings. You can check balance on a nail – the blade should lie horizontal. 

But it’s actually better to replace it than sharpen it. New blades aren’t expensive, but they’ll give you the feel of a new lawnmower.

4. Mower Vibrates Heavily

Excessive vibration during operation signals several possible problems. First and most common – damaged or unbalanced blade. If the blade hit a rock or tree root, it could have bent. Even slight deformation creates imbalance.

Second reason – loose engine mounts. In self-propelled mowers like MTD or Craftsman, the engine attaches to the frame with four bolts through rubber bushings. Over time, rubber loses elasticity, bolts loosen. Tighten all mounts and check the condition of rubber shock absorbers.

A bent deck (mower housing) is harder to fix. Here you need to assess the damage scale – sometimes it’s easier to replace the whole assembly than to straighten it out.

5. Self-Propel Drive Issues

Self-propelled mower stopped moving on its own or moves in jerks? First check the drive cable. It connects the handle lever to the clutch mechanism near the wheels. The cable can stretch or fray at the bend point.

Adjustment is simple: where the cable connects to the lever, there’s an adjustment nut. Tighten the cable until the slack disappears. If the cable is frayed – replacement needed. New cables run $8-15.

In models with an engine drive (via a belt), the belt itself may break or the tensioner may loosen. Check the belt visually; cracks, tears, or exposed reinforcing threads signal that it needs replacement. Lawn mower repair parts for drive systems are usually standardized and fit many models, which simplifies the search for the necessary part. UDC Parts, eReplacementParts, and PartsTree stock parts for most mower brands.

6. Electric Mower Shuts Off From Overheating

Electric mowers have different issues. Main problem – motor thermal protection triggering. Motor shuts off after 10-15 minutes of work, you have to wait for it to cool down.

The reason is usually overload. Electric mowers like Bosch Rotak or Gardena have limited power – typically 1300-1800 watts. If you’re cutting very tall or wet grass, the motor works at its limit and overheats.

Solution – don’t push the mower beyond its capacity. Better to cut tall grass in two passes: first at maximum height, then lower the deck. Also clean the ventilation slots in the housing – holes clogged with grass worsen cooling.

If thermal protection trips even with short grass, motor brushes might be worn. Replacing them requires disassembling the housing, but the procedure isn’t complicated and is described in the manual.

7. Broken Starter Rope

Gas mower won’t start because the pull cord snapped? Replacing it is doable on your own, though it requires care.

Remove the starter cover (3-4 bolts). Inside – a spring, spool with cord, and ratchet mechanism. First carefully release the spring tension, otherwise it’ll unwind sharply. Wind new cord onto the spool (3-4mm diameter, about a meter long), thread it through the hole in the cover, tie on the handle.

Then tension the spring: rotate the spool 5-6 turns in the winding direction and lock it. Test operation – cord should pull out smoothly and return cleanly. Tecumseh starters have a pretty stiff spring, requiring pre-tensioning.

8. Torn Grass Bag

Collection bag ripped at the seam or wore through? Many just toss it and mow without the collector, but this creates extra work – raking up clippings.

Small holes and tears can be repaired with nylon thread. Make the seam double so it holds when the bag is full. For large damage, you can buy a universal grass catcher or order an original for your model.

Fabric collectors repair easier than rigid plastic ones. Plastic boxes often have broken mounts or develop cracks from impacts. Cracks can be glued with epoxy or welded with a soldering iron through reinforcing mesh.

9. Oil Leak

Oil spots under the mower after work mean a seal has failed. Most often oil leaks through a worn crankshaft seal or through the crankcase sump gasket.

The crankshaft seal is a rubber ring that seals where the shaft exits the engine. Over time, rubber hardens and loses elasticity. Replacing the seal at home is possible, but you need to remove the blade, pulley, or clutch depending on design. Pry out the old seal carefully, press in the new one with a drift or socket of suitable diameter.

If it’s leaking through the sump, check the oil level. Overfilling creates excess pressure, and oil squeezes past the gasket. Check level with dipstick when engine is cold on level ground. Drain excess oil through the drain plug.

10. Clogged Discharge Chute

Mower runs but grass doesn’t discharge, clumping under the deck instead? Blades spin in a mass of clippings, engine load increases, you smell burning belts.

Problem is a clogged discharge chute. Wet clippings accumulate on the deck’s inner walls, especially when cutting tall or damp grass. Makita models with side discharge have a chute that narrows at the exit – that’s exactly where blockage forms.

Cleaning is easy: tip the mower over, use a wooden spatula or scraper to remove grass remnants from the deck and chute. Better not to use metal tools – you might scratch the protective coating, and corrosion will spread faster.

To prevent sticking, spray the inside of the deck with silicone. This creates a slippery coating that grass doesn’t stick to as much. Reapply every 2-3 weeks of active mowing.

Prevention Beats Repair

Many breakdowns are easier to prevent than fix. Regular maintenance extends equipment life several times over. Basic procedures take 30-40 minutes after every 20-25 hours of operation.

Change engine oil once per season or after every 50 hours of operation. Dark oil with a burnt smell contains combustion products that speed up cylinder-piston wear. Pour in SAE 30 oil for four-stroke engines or special mower oil.

Check air filter before each mowing. A clogged filter is the main cause of fuel waste and power loss. Tap out paper filters, wash foam ones with warm soapy water and dry thoroughly.

Sharpen blades 2-3 times per season or more often if there are lots of hard objects on your property. Sharp blades reduce engine load and fuel consumption by 15-20%.

Most lawn mower malfunctions don’t require complex repairs. Understanding basic operating principles lets you quickly locate problems and fix them with improvised means. Main thing – don’t put off minor breakdowns, because they quickly grow into serious damage that does require professional service.