I just bought a new lawnmower, but I probably could have saved myself $160 if I had done some simple maintenance chores on my old lawnmower first.
Before starting up the lawnmower, always check the oil level and make sure the oil is somewhere between the add and fill line. If there's no oil in the engine, the engine will seize because the pistons will get so hot that they'll literally weld themselves to the cylinders. But if there's too much oil in the engine, you'll notice the loss of power, and you will need to drain off some of that excess oil.
Once a year, clean the air filter, or just replace it if the air filter is too dirty to get clean. A dirty air filter will cause a loss of power to your lawnmower engine and will result in frequent sputters and stalls while you're cutting the grass.
Use fresh unleaded gasoline. If you had done your autumn lawn mower maintenance correctly, you will have run your lawn mower until it was completely out of gas before storing it for the winter. Old gasoline loses its combustion potency, especially when it's been frozen and thawed several times over the winter. Usually when I've had problems starting up my lawn mower for the first time in the spring, it's been because I was using last year's gasoline.
Once a year, change theengine oil. The oil in your lawn mower engine should look just like the oil that came fresh out of the bottle. Oil will break down naturally due to heat and friction, and a thick black sludge will start to form in your engine if you don't change the oil on a regular basis. This thick, black sludge can cause your lawnmower engine to seize up when it gets too hot.
Once a year, check and/or replace the spark plug and spark plug wire. A bad spark plug or a disconnected spark plug wire will result in your engine not being able to start. If your lawnmower engine will start, your spark plug and spark plug wire are probably fine for another season.
Once a year, sharpen the lawn mower blade. I like using a bench grinder to sharpen lawn mower blades, but a hand file will also work. A dull lawnmower blade will give you an uneven cut, and you'll find yourself going over the same area a few times just to make certain all of the weeds are the same height.
If you've done all of your maintenance chores and your lawn mower still won't run correctly, then it's probably time to hire a repairman or buy a new lawn mower.