Riding Lawn Mower Loses Power With Blades Engaged

If your riding lawn mower loses power with blades engaged, there are a few things that you can check on the machine.  Furthermore, there are some conditional variables that we need to discuss as well.  Read on to get your machine running properly again.

Machine Variables

Let’s start with the machine first because we can more or less control these conditions ourselves.  In general, a riding lawn mower needs three things to perform appropriately:

• Air/fuel mix
• Compression
• Spark

Whenever your  machine is not performing adequately, these are the three things that you need to check.  If your riding lawn mower loses power with blades engaged, definitely start here.

Tools Needed (Commissions Earned)

Compression

For the sake of this article, I’m mentioning compression first.  That’s because it’s a black and white situation and it’s easy to test.  You either have compression, or you don’t.

All you need is a simple compression test kit.  They’re inexpensive and handy to have for diagnosis.

Simply remove the spark plug and insert the correct fitting from the compression test kit into the spark plug hole.  Make sure to remove the spark plug from the boot so you don’t accidentally ground it.

From here, just connect the gauge to the fitting and turn the machine over.  Read the pressure that the gauge displays.  For proper compression, the engine should be around 90 psi.  If it’s less than that, there’s a good chance your machine is running inefficient – if at all.

Poor compression necessitates an engine overhaul; there’s no other option.  The cause may be a poorly seating valve, worn piston rings, a blown head gasket or a host of other issues.

For the sake of this article, we’re going to assume that the compression tests appropriately and move on.

Spark

With a spark tester you simply attach it in line between the spark plug and the plug hole.  When you crank the machine, the tester should light up.  The brighter it lights, the more adequate the spark is.

If it doesn’t light at all, then you know there’s an ignition problem with the coil or the plug itself.  Even if it’s weak, inspect the plug.

Is it dirty or contaminated?  Is it wet or damaged?  Take some time to inspect the spark plug and make sure the gap is set correctly.  This depends on the machine, so look up the specs for your riding lawn mower.

Air/Fuel Mix

Perhaps the most complicated issue with riding lawn mowers is the air/fuel mix.  That’s simply because it contains more variables.

The engine needs the appropriate mix of air and fuel to run efficiently.  This is determined by the carburetor, the fuel filter and the air cleaner, so inspect these components.

If the fuel filter is yellowed or dirty, replace it.  I typically replace mine annually anyways.  They’re inexpensive and easy to swap out.

Make sure that the air cleaner is not full of debris.  That is exactly what the air cleaner is designed to do – filter the air coming into the machine so debris doesn’t end up inside.  

By doing so, it can restrict the amount of fresh air that’s allowed in, thus offsetting the appropriate air/fuel mix.

Likewise, a dirty carburetor will not allow adequate fuel into the machine.  This will also offset the mix and result in a poorly running riding lawn mower.

Environmental Variables

Granted, not all of these issues are directly resultant from the environment, but they are related.  Basically, anything that causes too much load or strain on your engine will result in a loss of power.

If a riding lawn mower loses power with blades engaged, I would definitely recommend looking at these issues.

Deck Height

The deck height determines the depth of cut, or the volume of grass that is being cut in one pass.  Essentially, the lower the deck, the more grass the machine is trying to cut.

The more grass, the harder it is on the engine.  If you attempt to cut too much grass at once, the resistance will be so great that it can cause your machine to bog down and lose power.

If the grass is deep, set the deck higher and do a full pass.  Then come back a day or so later and cut it again at a lower depth.

In general, it’s bad for the lawn to cut more than 1/3 the depth of the grass at one time anyway.

Clogged Deck

This will also add increased resistance to the machine.  As you cut, the grass slowly builds up on the underside of the deck.  If left untreated, not only will this cause your machine to stall out, but it can also destroy the deck.

Since grass contains moisture, once it’s caked on the underside of the deck that moisture has nowhere to go.  The result is that it will simply rot out the deck of the machine, and this can happen quicker than you’d think.

That’s why I recommend cleaning the deck after every cut.

Wet Grass

Wet grass is generally harder to cut than dry grass.  This adds increases resistance and load to the riding mower which can result in a loss of power.

Furthermore, wet grass can substantially increase the buildup underneath the deck.

I would advise against cutting wet grass if at all possible.  That being said, I know that it’s not always avoidable.

In those cases, make sure to do light cuts and do a thorough job cleaning the deck afterwards.

Dull Blades

Dull lawnmower blades cut the grass less efficiently than sharp blades.  That makes sense right?  As we’ve mentioned, anything that increases resistance can result in a loss of power.  This can certainly include dull blades, so make sure to keep them sharp.

Recap

There a host of variables that can cause a riding lawn mower to lose power with blades engaged.  Hopefully, after reading this article you can figure out which are plaguing you.

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