My Lawn Mower Is Hard To Start

Lawn mowers can be finicky machines. They can be easy to start one day and hard to start the next. In most cases it is a simple adjustment to make them easier to start.

This adjustment is often a valve adjustment. Over time the valve clearance become loose and will not allow the valves to open properly. If the intake valve does not open fully, a fresh charge of gasoline will not make it into the combustion chamber. If the exhaust valve does not open fully, the hot gasses will not be expelled out the exhaust pipe and it prevents fresh gas from coming into the combustion chamber as well.

An engine is basically an air pump. Air goes in and air goes out. Whenever that cycle is interrupted, it makes it hard to start the engine. Try adjusting those valves to their proper specification and see if it makes a big difference in the starting of that engine.

You should also check to make sure that the choke is working properly. An engine choke is a butterfly type valve and you close in the carburetor. When it is closed, it creates more vacuum inside the carburetor and pulls more fuel through it and into the engine. If the choke is not closing fully, then fuel will not be adequate enough for a cold start operation.

By adjusting the choke and valves, you should have an easier starting lawn mower.

My Lawn Mower is Hard to Start

This is a very common problem. You keep pulling the pull cord until it finally starts or you turn the key and crank and crank until it finally starts. Both result in the same hard starting lawn mower engine.

It comes down to a common few things that cause this problem. One is you are not getting enough fuel in the engine because the fuel pump is going out or there is an obstruction in the line, fuel filter or the carburetor.  Try turning the engine over on a riding lawn mower with the fuel line disconnected at the fuel pump outlet line and have a catch can waiting to catch any fuel that comes out. If fuel comes out readily, then your fuel pump is fine.

On a gravity fed system. unhook the fuel line at the carburetor and see if fuel comes out. You will need a tool to pinch the fuel line closed and they make a special one with smooth jaws for this. If you don’t have a way to stop the fuel from flowing, you will have a big mess to clean up!

If fuel is going to the carburetor, then pull the spark plugs and make sure they looks slightly wet with fuel. If they are, the problem is most likely your valves are out of adjustment.

On a push or self-propelled lawn mower, to test for fuel getting to the engine, pull the cord or turn the key on an electric start a few times and then remove the spark plug and see if there is fuel on it. If there is, your valves are probably out of adjustment if it is an overhead valve engine.

Another common item to cause this problem is the choke not set properly or it is malfunctioning. Check to be sure it is closed when you are starting the engine and slowly opening as the engine warms up.

Blown headgaskets can also cause hard starting and low cylinder pressures due to bad piston rings or valves that are not seating well. The carburetor may not be venting either and throwing a lot of fuel into the engine flooding it. The needle and seat may be failing an flooding the engine as well.

Bad fuel or water in the fuel can also cause hard starting in your lawn mower.

Check each system one at a time to help narrow down what the problem is and then find out which specific component is the culprit to solve my lawn mower is hard to start problem.