Just so FRUSTRATING!! Cutting tall heavy grass, especially if it’s wet, will keep you busy clearing the chute all day.
So what’s going on, why does my mower chute clog? The most common reason a mower chute clogs is because the grass is too heavy, but there are lots of other reasons:
- Poor Cutting Conditions
- Deck Too Low
- Dull/Damaged Blade
- Deck Grass Build-up
- Throttle Too Low
- Poor Engine Performance
- Damage To Deck
- Deck Belt Slip (Tractor)
- PTO Slip (Tractor)
- Using Mulching Blade
Lawnmower grass catcher troubleshooting is straightforward, most are common problems and easy to solve. In this guide, we’ll look at all the most common causes.
Grass height, weather conditions, and a worn blade will be the most obvious reasons for the tractor or walk behind mower clogging. Very often, a dull, damaged, or worn blade is the root cause of a clogging chute.
If you need video help, check out the “Mower blade sharpening video” it walks you through the whole process step by step, from examining the blade, sharpening both on and off the mower, blade removal, blade balancing, refitting including using a torque wrench to tighten blade bolt to spec.
Conditions & Chute Clogging
As a guide, you should cut no more than 1/3 off a blade of grass at once. For best results, a mower shouldn’t be cutting more than an inch of grass, and the best lawn height is about 3″. Cutting regularly keeps the workload on the machine to a minimum and it’s easier on your lawn.
Weather makes a big difference, obviously if the grass is damp the mower is going to struggle to perform. But I understand, sometimes it’s necessary to cut wet grass when you need to get the job done.
A clogged chute can of course be a symptom of an underlying problem. Clearing the chute may not resolve the issue. Grass build-up or damage to the underside of the deck can cause the grass to catch and clog. The underside of the deck should be smooth so that the grass moves freely around the deck, up the chute, and into the bag.
Chute – Clearing the chute may not solve the problem. Check the chute for damage or old dry grass build-up.
Clean – Old grass on the deck can cause problems. Regular cleaning will prevent build-up and prolong the life of your mower.
Deck Wash Port – Clean the underside of the deck at the end of the season, as the acid in the grass eats away at the metal over the winter. Most mowers will have a garden hose connection on the deck, simply connect your hose and run your blades to clean the underside of the deck. This does a reasonable job at cleaning.
The wash-out port isn’t fitted to all mowers. It does a pretty good job of cleaning the underside of the deck.
Hose – Move your mower to a suitable location as it leaves a bit of a mess. Just attach and turn on a garden hose. Start your mower to engage blades. Run until water runs clear – simple!
Deck Coating – After cleaning the deck and allowing it dry thoroughly, spray on a coat of WD40, it’ll help protect the deck over the winter and also help keep the deck grass-free in the spring. Better than that is applying a non-stick film, it works pretty good and it’s easy to apply.
The best in the business – DuPont Teflon non-stick dry film, and you check out the price on Amazon.
Clean – Lift the front of your tractor, secure it well before climbing under. A wire brush and paint scraper do the job.
To Prevent Clogging
To help prevent clogging, three options are common:
Option 1 – Quick fix is to 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 deck with bed liner. Works on tractors, riders, and walk-behind mowers. Check out the video here.
Check Your Grass bag
A clogged grass bag is a common problem. Tractors and walk behind mowers often get cleaned at the end of the season (well some do) but bags rarely do. Symptoms of a clogged bag are not collecting or only a half-filled grass bag.
Examine your bag/box, when held to the light you should be able to see through it. A stiff brush will remove the old grass or use a power washer.
Consider buying a new grass bag if damaged. They are available to purchase usually with or without the frame. Check if the bag/box sits correctly against the mower body. If it’s loose, the air and grass flow to the bag will leak.
Bag – Thatched grass on the inside of the bag is a common issue. It prevents airflow through the bag which in turn prevents grass from entering the bag.
Clean – As a rough guide you should be able to see through the bag. A stiff brush or better a pressure washer does a great job.
Check For Blade Damage
Two types of blades are common, the lift blade and the mulching blade. They are fitted to tractors, ride-on, and walk-behind mowers. A defective blade can cause vibration, uneven cutting, and poor grass collection.
No need to tell you a bent blade is dangerous and should never be repaired. A new blade, bolt, and washer is the way to go.
Examine – Check your blades for damage, misalignment, bent or broken tips. Your blade is the business end of the mower and needs to be in top condition. Defective blades can cause vibration, uneven cutting, and poor grass collection. A mowing blade may look OK, but they do wear.
Mowing blades are engineered to cut and move grass, as they wear they become much less efficient. A worn blade will cause clogging.
Timed Blades – Some deck setups will have an overlapping cut, although more common on lawn tractors than walk-behind mowers.
Toro Timemaster walks behind the mower has a timed blade set up. To achieve this the blades must be fixed at a set angle in relation to each other. This is done by using a toothed timed belt.
If one of the blades hits an object, the blades go out of time or the belt can break. When the blades are out of time, bagging quality suffers and a clogging chute is a symptom. In addition, badly timed blades usually damage each other. I wrote this detailed guide including pictures to help you replace your “Timed deck belt”.
Dull or Worn Blade
A dull or worn blade will cause clogging, as the carefully engineered blade wears, the trailing edge is less efficient at moving the clippings. The leading edge will also be worn from grit and debris, and sharpening sessions will likely have changed its shape.
The average mower should get a new blade every 3rd or 4th season. If the blade is in good overall condition, go ahead and sharpen it.
The Lift blade is also known as the 2 in 1, so-called because it bags and discharges. Lift blades vacuum the grass upright, before cutting and moving the clippings to the bag. Lift blades are specially designed for collecting grass and come in low, medium, and high lift.
2 in 1 Lift Blade
Lift meaning sucking power, a higher lift blade will require a more powerful engine. The lift is created by curving upwards of the trailing edge of the blade.
If you like bagging – You need a lift blade.
A true Mulching blade is designed to cut grass, circulate it around the deck cutting it several more times, and dropping it back onto the lawn as fine clippings.
You’ll know a mulching blade when you see it, the leading edge isn’t straight, it curves up and down. This results in several cuts to the same grass blade but at different heights – fine clippings.
If you’re not interested in mulching, then remove the mulching blade and fit a lift blade. It will always bag better than any hybrid mulching blade.
3 in 1 Blade
A true Mulching blade is not designed to collect. That got engineers thinking – Meet the hybrid mulching blade or 3 in 1. It attempts to do it all, mulch, bag, discharge, however, we all know it can’t be excellent at everything, and it isn’t.
Mulching has become quite popular, and manufacturers have responded by making a blade that tries to do it all but doesn’t quite succeed.
Check out the blade replacing video here and if you need new blades check out the Amazon link below.Amazon Lawnmower Blade
Engine Performance Problems
It’s also worth considering, if the throttle is 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.
I wrote these guides to help you tune up your own mower, it includes an oil grade chart and quantity for your engine, check out:
Stale gas is the number one most common cause of poor engine performance. It’s caused usually by letting gas sit in the mower over the winter. The bad gas can damage the carburetor causing 100$$ in repairs and it’s not covered by your warranty.
This problem can be avoided by using a gas stabilizer, you won’t have to use it all season, just at the tail end. It’s simple to use, just dump the bottle of gas stabilizer into your gas tank and run the engine to mix it throughout the fuel system, that’s it. You can find a link to the fuel stabilizer I use here and a video on how to use it here.
The fix for bad gas – remove and clean the carburetor, if it’s badly corroded, you’ll need to replace it.
I wrote these easy-to-follow guides including pictures on carburetor cleaning, it will help you find your problem and fix it fast.
Tune-up – Mowers like a tune-up at least once per season.
What Is Power Take Off (PTO)?
The PTO clutch assembly will not be fitted to all mowers, and so this may not be applicable. It’s fitted mostly to tractors, ride-on, and larger walk-behind mowers.
PTO clutch is a unit fitted to the end of the crankshaft. The deck belt wraps around the PTO pulley, its function is to apply the power of the engine to the blades when a switch or lever is operated.
The PTO clutch when worn will slip reducing power to the blades. This will be especially noticeable in taller grass. The PTO if fitted will be manual or electromagnetic.
If manual it will likely have a lever and cable to operate – check that the cable is pulling the PTO. Both types can’t be repaired, they must be replaced.
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.
Fitting – Replacing the PTO isn’t difficult, air tools make it look really easy.
Tractor Belt Wear Problems
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.
Worn – A cutting deck belt that’s slipping will be less efficient at collecting. Check the belt for proper tension, cracking, glazing or contamination.
Damaged – Damaged belts will cause vibration and poor general performance. A typical deck belt might last 3 – 4 years.
You may find these links useful:
Walk behind mower troubleshooting
Why is my lawn mower leaving a strip of grass?
Why is my lawnmower spitting out grass? Common reasons for grass trailing is grass-bag or box not sitting on the mower deck correctly. Check for gaps around the bag/deck interface and holes in the bag.
Grass not going into the lawnmower bag? When your mower isn’t filling the grass bag, first try cleaning the bag, if that doesn’t help, replace the cutting blade.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.