What Causes a Lawn Mower to Lose Power Going Uphill?

Although gas-powered push lawn mowers are made for home and commercial yard use, you may have hills that also need cutting. Unfortunately, you can own a mower that cuts just fine on level grass but loses power when going uphill. While there are multiple parts and systems to troubleshoot, a few adjustments or minor replacements will keep your mower functioning on flat and hilly grass.

Your gas tank should be full when mowing a hill. Low gas levels could still get your mower started. But if your tank is located near the back of your mower, pushing it uphill could move low gas levels to the back of the tank and away from the carburetor.

Your mower's carburetor is responsible for mixing the fuel and air to create an ignitable gas, which powers the engine's pistons. Some mowers have a choke switch that allows additional fuel to enter the carburetor. If the choke is malfunctioning or your carburetor is dirty, there may not be enough fuel vapors entering the engine to support the extra push needed for the hill. Damaged seals or gaskets on the carburetor could also interfere with operation.

The mower's spark plugs fire about 1,000 times a minute during engine operation, igniting fuel vapors as the pistons move upward. When a spark plug becomes fouled, the tips become coated with fuel, carbon, oil or dirt. This interference limits the ignition power needed for mowing on level or uphill surfaces. Maintain your spark plugs by changing them every season or regularly removing and cleaning the tips.

Once your mower's gas is burned, it has to exit properly or the engine can seize. The muffler is where the expelled gas exits. If the muffler gets clogged from debris or fluids spilling into it, the engine will malfunction and lose power. Clean your muffler every season or if your mower expels colored smoke.

Although your blade's rotating speed may be sufficient to cut level grass, blades with significant corrosion or interference can cause it to lose power uphill. The mower blades rotate hundreds of times per minute during full operation. If there is any additional weight on the blades from grass or mud, it can slow down the number of revolutions. Rusted hardware on the rotating shaft can also slow down your mower.