The first sunday of spring usually brings A certain sort of panic. You haul the mower out, yank on the cord, and all you get is the empty gurgling cough of a dead engine. It feels like a personal frustration, but no: Briggs and Stratton engines don’t do this for nothing.
There’s a simple mechanic’s logic behind them, and they can usually tells exactly who did what wrong. Silence is rarely mystical; it’s simply one link in the firing triangle that’s been left dangling. Prevent an expensive repair bill by understanding what’s wrong when your mower doesn’t crank over.
How to Diagnose Why Your Mower Won’t Start
Diagnosing the Firing Triangle
The problem come down to three simple things: compression, spark, and fuel. Without at least one of these, it will not start. With some patience and some basic tools, you’ll be able to diagnose most problems yourself.
Fuel System and Carburetor Issues
Don’t worry, you don’t have to be a mechanic to fix it; just follow where the power goes. Most of the time it’s simpler than you think, but the first place to look? The fuel system.
Gasoline separates when exposed to moisture. And that’s what ethanol-based fuels do, attract moisture. That leads to a gummy gasoline, which gums up the carburetor, the number one killer of small engines.
If yours spent the winter sitting, that gas is probably toxic sludge at this point. Drain it. Fill it with fresh mix.
A cracked fuel line or clogged fuel filter is another possibility. They’re cheap fix that solve most no-start cases. So check them first.
Inspecting the Spark Plug
So if your engine won’t fire up on new fuel, you work your way down to the spark plug. It’s a tiny bit of metal and ceramic that makes up the ignition system. Take it out, inspect the gap (typically around 0.030 inches on most Briggs) and replace it if needed.
An oiled-up spark plug or one with carbon buildup won’t fire. And even if it appears fine, swap in a proven good spark plug. Cost?
Cleaning the Air Filter
Nothing but time and the elimination of another big variable. Surprisingly, folks rarely do this, but it makes a difference. The air filter might not be directly related, but it is essential because air are necessary to burn fuel properly in an engine.
Dust and other junk like grass clippings in the air filter starve the engine of oxygen. This cause the mixture to become rich, choking off combustion. Replace or clean your filter.
And while you’re there, check the port where the spark plug fits for any packing of grass. Grass can literally pack into the deck area and keep the piston from moving. Getting the air path clear is often what’s needed for a smooth idle instead of silence.
Checking Safety Interlocks and Compression
And lastly, do the safety interlocks. Most mowers these days has switches that stop the engine if seat isn’t in use, or the blade is engaged. Those switches fail over time.
Temporarily bypass those to see if that’s what’s happening. It is a little thing, but it is an important one. If it has no safety lockouts, good spark, good fuel and clean air, then maybe there’s something else wrong with the engine, like low compression, which could indicate a more serious problem inside.
But first make sure of the basics, and don’t assume the worst. The spring will come around again and your mower will be waiting.