Lawn Mower Grass Catcher
Troubleshooting

Stopping every 5 minutes to clear the underside of the mower isn't much fun! Grass catcher problems can be so annoying.

 

Troubleshooting a lawn mower grass catcher? Common grass catcher problems like, clumping, clogging, uncut grass and a grass bag that won't fill are caused by:

 

  • Grass Too Tall/Wet
  • Deck Too Low
  • Dull/Damaged Blade
  • Deck Grass Build-up
  • Throttle Too Low
  • Moving Too Fast
  • Poor Engine Performance 
  • Damage To Deck
  • Deck Belt Slip (Tractor) 
  • PTO Slip (Tractor)
  • Wrong Blade 
  • Grass Bag Matted

In this guide I will cover all the most common grass catcher problems and the solutions.

Mower Chute Clogs

I live in Ireland and it rains, a lot, sometimes it rains persistently, and if you need to cut grass, then you have to cut wet grass. Grass chute clogging is usually caused by cutting conditions but is also commonly caused by a worn cutting blade.

 

The blade is the business end and it needs to be in tip top condition. 

 

mower chute

Chute

A clogged chute can of course be a symptom of an underlying problem. So clearing the chute may not solve the problem.

Check the chute for damage or old dry grass build up.

mower deck

Clean

Old grass on the deck can cause problems.

Regular cleaning will prevent build up and prolong the life of your mower.

mower blade sharpening

Sharpening

A dull blade will solve lots of cutting and collecting issues.

Wet Grass

It's much heavier than dry grass obviously, and won't be thrown as far into the grass bag/box by the labouring engine. It also sticks to the underside of the mower, causing clogging, and preventing the grass catcher filling.

 

Bottom line, mowers don't cut damp/wet grass very well, especially if it's tall.

 

 

mower cutting wet grass

Wet

Most mowers will find these types of conditions challenging.

Tall Grass

How about the cutting height, it may be set too low. I know this sounds obvious but try lifting the deck height, and if you want a tighter cut - drop the deck and cut again. Ideally your mower shouldn't be cutting more than an inch of grass, ask it to do more and cut quality suffers.

 

My best advice, cut more regularly, keep your mower deck clean and free from dry grass. Consider coating the underside of your deck with Teflon Non-Stick coating, it helps reduce grass clogging.

 

mower deck clean

Tall Grass

Tall grass is hard on a mower, especially if your asking it to cut the lawn tight with just one cut.

Tall grass will cause the mower to clog.

Mower deck Mower deck

Protect

To help prevent clogging:

Option 1 - Quick fix is spray the deck with WD40, it does help but it won't last.

Option 2 - Spray deck with DuPont Teflon coating.

Option 3 - Spray the the deck with bed liner, my preferred option. Works on tractors, riders and walk behind mowers.

What Is Mulching?

As you know mulching blades chop grass very finely and drop it back onto the lawn where it helps feed the lawn. Mulching blades are designed specifically for this task, but they can cause lots of clogging problems, especially if the grass is long or damp.

 

Mulching blades just don't move grass efficiently, because they're not designed to. They work best when the grass is cut dry, regularly and in small amounts.

 

mower grass bag

Mulching Blade

Mulching Blades aren't designed to collect.

Ride-on mower battery test

Tall & Wet

Mulching tall wet grass won't work, the blade is designed to cut just small amounts of grass at a time.

Hybrid Mulching Blade

As you know a true mulching mower doesn't collect, its function is to finely chop and drop the clippings. This type of cutting is convenient, it's a lot less work than emptying a grass bag, which gave mower manufacturers an idea.

 

The Hybrid Blade (3 in 1) - a mower blade that does it all, collects, mulches and discharges. Well, it does an OK job, but if conditions become challenging the quality does suffer, especially if conditions are wet.

 

The complaint I hear most with the 3 in 1 mulching blades - won't fill the grass catcher. The solution - remove the mulching blade and fit a lift blade.

 

If you don't want to mulch, change your blade for a lift blade, you will eliminate lots of clogging, clumping and half filled grass bags.

 

mower 3 in 1 blade

3 in 1

The Hybrid mulching blade, kind of ok at everything.

Lift Blade

Lift blade also known as the 2 in 1, so called because it bags and discharges. The lift blade vacuums the grass up right, before cutting and moving clippings to the bag.

 

They're designed for collecting grass and are available in low, medium and high lift. A higher lift blade will require a more powerful engine. The lift is created by the curving upwards of the trailing edge of the blade. The higher the lift the better the bagging.

 

mower blades

2 in 1

If you love bagging - You need a lift blade.

Honda 3 in 1

The Honda Hybrid mulching blade is the best in the business, unfortunately it can't be fitted to other mower makes. The reason the Honda is so good at mulching and collecting - twin cut blade set up.

 

Twin stacked blades - One blade mulches and the other moves the clippings. Smart!

 

mower blades

3 in 1

Honda's answer is 2 blades, one for mulching and the other for moving.

Grassbag Won't Fill

A grass bag/box that doesn't fill, has a few likely causes. The obvious ones: clogged chute; thatched grass bag; damaged or worn blade; insufficient throttle; poor engine performance.

 

Grass-bag

A thatched grass bag is a common problem. Mowers often get cleaned at the end of the season (well some do) but bags rarely do. Examine your bag/box, as a guide, when held to the light you should be able to see through it.

 

If the air can't pass through the bag, then grass won't be carried into the bag. A stiff brush will remove the old thatched grass or better, use a power washer.

 

mower grass bag mower chute

Cleaning

Stiff brush or a power washer does the job.

Chute Clogs

A clogged chute can be a symptom of an underlying problem. So clearing the chute may not resolve the issue. Check the chute for damage or old dry grass build up.

 

Grass build up or damage to the underside of the deck can cause the grass to catch and clog.

 

mower chute

Chute

Chute keeps clogging.

Deck Clean

The underside of the deck should be smooth so that the grass moves freely around the deck, up the chute and into the bag.

 

DuPont make a Teflon Non-Stick coating which helps reduce grass clogging.

 

mower deck mower deck mower deck wash out port mower deck clean

Cleaning

Move your mower to a suitable location as it leaves a bit of a mess

Just attach and turn on garden hose. Start your mower to engage blades.

Run until water runs clear - simple!

If you don't have a wash out port or garden hose, no problem.

Turn your mower over air filter side up, use a paint scraper and wire brush. It works great.

Why The Grass Trailings?

Grass trailings are commonly caused by a poor fitting or damaged  grass catcher. If you find your grass catcher is damaged, consider buying a new one, they're available to purchase with or without the metal frame.

 

Check if the bag/box sits correctly against the mower body. If it's loose or damaged, the air and grass flow to the bag is compromised.

 

If all is well with the grass catcher, go ahead and replace your blade.​

 

tractor mower trailings tractor mower trailings

Trailings

Trailings are really annoying, check that the bagger is closing snugly.

Check For Blade Damage

A defective blade can cause vibration, uneven cutting and poor grass collection. Examine your blade, checking for damage, misalignment, bent or broken trailing/leading edges.

 

Sharpening

Blades need to be kept sharp. I recommend about twice per season or more depending on terrain. Obviously if your blade is dull it can cause all sorts of problems, including blocked chute and grass catcher issues. 

Ride-on mower blade

Impact

When blades hit something hard, well, you know! The damage causes vibration and all sorts cutting issues.

mower blade damage mower blades

Bent

Bent blades can't be repaired, just go ahead and replace them.

What Is PTO Slip?

The blade clutch or PTO (Power take off) won't be fitted to all lawn tractors, but it's easy to locate, it lives right under the engine. A clutch system isn't common on walk behind mowers but Honda and Toro offer them on the higher end models.

 

It may be manual or electric, either way, its job is to lock the engine crankshaft to the blade deck pulley, when you engage the blades on button or lever. The clutch like a clutch in a car, will wear out, and when it does it causes the connection between engine and deck to slip.

 

Symptoms include poor grass collection, uncut grass and sometimes a burning smell.

 

Ride-on PTO

PTO

Check the PTO system. The manual version is engaged by a cable. It lives on the crankshaft, right under the engine.

Check that the cable is pulling the pto lever all the way.

mower PTO

Fitting

Replacing the PTO isn't difficult, but air tools would make it really easy.

Check Deck Belt Condition

Belt wear is also a common reason for a chute to clog, check the deck cutting belt for damage and general wear & tear. A new belt will transfer more of the engine power to the cutting blades and will improve the cutting and bag filling performance.

 

Belt types and lengths will be specific. Some brands will only work well using Oem (Original Equipment Manufacturer) belts, check out "Mower belt replacement". 

 

mower deck belt

Worn

A cutting deck belt that's slipping will be less efficient at collecting.

Check the belt for proper tension, cracking, glazing or contamination.

Mower deck belt

Damaged

Damaged belts will cause vibration and poor general performance.

A typical deck belt might last 3 - 4 years.

Check Engine Performance

Its also worth considering, is the throttle set correctly, it should be set to fast/run when cutting. Is the engine running as it should. If the engine power is reduced the mower may still cut well, but will be less efficient at collecting. 

 

A small engine tractor or walk behind mower should have a tune-up at the beginning of every season, regardless of how well it might be running.

Belt types and lengths will be specific.

 

Some brands will only work well using Oem (Original Equipment Manufacturer) belts, check out "Mower belt replacement".

 

Check out:

 

"Lawn tractor tune-up"

"Lawn mower tune-up"

 

Bad Gas

Old fuel is the number one cause of poor engine performance, use a gas stabiliser over the winter to help protect your lawn mower carburettor, check out "Carburettor troubleshooting".

 

 

lawn mower

Tune-up

Mowers like a tune-up at least once per season.

Related Questions

How does grass catcher work? A grass catcher works by collecting the grass that is thrown into the bag by the force of the mower blade wings. The grass catcher works best when the walls of the bag / box are clear so that the forced air from the blade can pass through it quickly.

Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.