Lawnmowers, notably push mowers, normally cut off when you cut thick or tall grass. It could indicate that you need to make adjustments to the mower. It also might indicate that you need to adjust your mowing schedule or perform basic maintenance duties on the mower.
Height Needs Adjusting
The design of lawnmowers allows them to cut the grass within a certain height range. Often, you can adjust the deck height, which adjust the height that the mower blade cuts the grass. If the mower keeps shutting off when you cut thick areas of grass, make sure the mower height is not set too low. Many mowers have wheel levers at each of the mower's four wheels, or another way to adjust the mower height. Stop the mower engine, raise the height and resume mowing. If the mower quits again, raise the deck higher, to the highest point if necessary, and continue mowing. Mow the grass again, sooner than you normally would, with the mower height lowered, to gradually bring the grass down to the proper height.
Discharge Chute Clogged
As you push the lawnmower forward through the thick grass, it is constantly shooting the cut grass out, through the discharge chute, normally located on the mower's right side. Continually cut thick grass and the mower might not have enough of a chance to discharge the cut grass before even more cut grass piles up. This built-up grass blocks the discharge chute and eventually jams the mower's spinning rotary blade, which shuts down the engine. Prevent this by stopping the engine yourself when you notice grass clippings clogging the discharge chute. Allow the blade to come to a complete stop, and clear out the discharge chute. Also, clean clippings off the underside of the mower deck after each mowing, to fend of buildup.
Need to Cut More Frequently
If the mower cuts off each time you cut a thick lawn, consider simply cutting the lawn more frequently. By doing this, you avoid the hassle of having to constantly make adjustments to the deck height, or having to watch the discharge chute like a hawk to prevent it from clogging. Ideally, to maintain the healthiest grass, cut down no more than one-third of the grass height each time you mow. Cutting the grass down too low opens it up to drying out. Also, don't overwater the grass, which helps cut down on the growth.
Mower Needs Basic Maintenance
If the lawnmower cuts shorter areas of grass with no problem, but shuts off each time you get to thick areas, make certain that you perform the necessary basic maintenance on the mower so that it operates at its best level. Check your owner's manual for the specific maintenance tasks that you should regularly perform. Specific maintenance duties normally include sharpening dull blades and changing dirty air filters. Ignoring these items can contribute to the mower shutting off in the thick grass.
Mower Lacks Horsepower
The lawnmower may just lack the needed horsepower to manage thick areas of grass. In this case, the mower will either shut off, or will miss a lot of the grass blades, causing you to need to go over the same spot twice. If necessary, obtain a mower with more horsepower.