Pre Repair No Start Checks


Mower Won't Start

Very often, it's something simple preventing your mower starting. This short video helps eliminate all the easy to fix stuff first.

Ignition system Section


Spark test

This video walks you through the process of checking your spark plug with and without a test tool. It also covers plug diagnoses and what each plug condition means. This video works for all mowers.

Armature

Armature provides the voltage to fire the spark plug, armature failure is common.

The video walks you through the process step by step, from checking the armature, checking for wiring short, fitting armature and setting the air gap. This video works for all mowers. 


Shear-key

A broken shear-key may cause backfiring, no start and pull cord recoiling sharply.

The video walks you through the process step by step, checking the shear-key, tapping flywheel, removing flywheel, torqueing flywheel. See "Repair Tools" on how to use a torque wrench. This video works for all mowers. 

Fuel System Section


Gas shot

This video shares a simple hack an old mechanic thought me, it's great for quickly diagnosing carburetor issues. This cool trick works for all mowers and any gas powered engine. 

Choke test

The video walks you through the process of identifying your choke type, testing it and performing common repairs. This video works for all mowers. 

Gas Bowl Clean

Very often the source of poor running and no starts is dirt or moisture in the gas bowl. In this video we'll remove, clean the gas bowl, fuel jet and syphon stale gas from the gas tank. This video works for all mowers. 

Carburetor Clean

A clogged carburetor is such a common issue especially after the winter hibernation. The best fix is to remove and clean or replace the carburetor. This video covers the whole process step by step and works for all mowers. 

Compression System Section


Compression test

Low compression will cause no or hard starting, it's usually a sign of engine wear and associated with burning oil and a smoky motor. However not all cases of low compression are terminal. In this video we'll run a dry and wet compression test and you'll understand what the different readings actually mean.

Valve Check

A valve that sticks open will prevent starting and is common in mowers that lay idle for a time. This video shows you step by step how to fix the issue in minutes. This video works for all mowers. 

Over View

You’ll find useful resources on this page, tips, links to tools, parts and supplies required to complete your repair.

My mower won’t start is the complaint I most commonly hear in the spring, just after the winter hibernation.

If that sounds familiar, then it’s likely your fuel system is filled with stale gas and so we’ll need to clean it out, it’s a common issue and is covered in these videos.

There are 3 main ingredients an engine must have in order to run (Ignition, Fuel and Compression). One of the 3 is at fault and in these videos we’ll find out.

To diagnose our fault, we’ll run simple tests along the way, the results of each test will guide us towards the root cause of our problem and of course the fix is included.

By the end of these videos you’ll be a pro!

Before working on your mower be sure to remove the plug wire to prevent accidental starting, see “Repair Safety Video”.

Resources

Briggs & Stratton – Most models take from empty .65 US quarts (.6 lts) 5W30 engine oil.

Honda engines – Most take from empty .58 US quarts (.55 lts) of 10W30 engine oil.

Kawasaki engines – Most take from empty .6 US quarts (.6 lts) 10W30 engine oil.

Kohler engines – Most take from empty .6 US quarts (.6 lts) 10W30 engine oil.

For exact specs see:

Briggs & Stratton spec

Honda spec

Kawasaki spec

Kohler spec

Tools & Parts

To nail this procedure you may need the following tools, parts and supplies.

WD40

This is first on the list for good reason, Wd solves a ton of problems. I won't work without it, because I can't. Picture links to Amazon.com

Ratchet Tool Set

Before we can do anything, we'll need tools. I've selected this set as I own some Craftsman tools and while I have worn some out, they did do a lot of work. So I expect this set will last the occasional user quite a long time.

This set carries both metric and standard sockets and that's important, because some mowers will have both type of fastener sizes. Set includes spark plug sockets. Picture links to Amazon.com

Gas & Oil Syphon

You'll find this tool really useful if you need to drain the gas tank, and you will if the gas is stale. The siphon will remove it without fuss or mess and it can be used for extracting the oil too. Picture links to Amazon.com

Gas Line Clamp

Some small engines will have a gas tap, which is really handy when removing the carburetor, stops gas flowing all over the shop. However most engines won't have one, these useful clamps simply squeeze the fuel line and prevent a spill while you perform surgery. Picture links to Amazon.com

Carb Cleaner

When cleaning your carburetor you'll need this stuff. Gumming is a sticky substance that's hard to shift. The carb cleaner will remove it, however if your carb is really bad, save yourself some work, go ahead and buy a new carburetor. Picture links to Amazon.com

Cleaners

You'll find these nylon brushes super useful when it comes time to clean those tiny passageways of the carburetor and jet. Use these in conjunction with the WD Carb cleaner. Picture links to Amazon.com

Gas Stabilizer

Mix this with the gas when winterizing your small engine. Gas isn't what it used to be, it goes stale, in some cases after just one month. Bad gas causes gumming and that's a carburetor killer. Stabilizer will save you money and stress in the long run. Picture links to Amazon.com

Gas Can

Briggs and Stratton refuel can. These guys got it right, I like it a lot, it offers press button control, no fuss no mess and no funnel required. Picture links to Amazon.com

DVOM

Every home needs a Dvom (Digital Volt Ohm Meter). It's used to check for continuity in lawn mower wiring, and for voltage when there's a battery fitted. But don't use this tool to check spark, that will kill it. I use mine everyday. I have the previous model to this and it's still doing its job. Picture links to Amazon.com

Flywheel Puller

Now this tool is a must have if you're removing the flywheel. Why would want to remove the flywheel? Sometimes the flywheel key shears, it stops your engine starting. The key is really cheap and it's easy to fix when you've got this tool. Picture links to Amazon.com

Tap & Die set

Used to cut threads. Many flywheels are not threaded which a right pain in the jacksie, but this Gearwrench kit makes short work of threading. I especially like the ratcheting T handles. Picture links to Amazon.com

Ignition Tester

This tool is used to check both the spark plug and the coil for spark. Sure you can check the spark without the tool, but it's not as good, the tool is designed to stress the whole ignition system. Picture links to Amazon.com

Feeler gauge

The ABN 26 blade feeler gauge set is marked in SAE and metric. You'll need this set to adjust valve lash and is useful when setting armature/coil air gap. You can also use it to gap spark plugs. Picture links to Amazon.com

Plug Gapper Tool

This tool isn't strictly necessary if you have a feeler gauge, but it's a lot easier to handle. If you haven't guessed. You use this tool to check the gap of your spark plug, simple effective tool. Picture links to Amazon.com

Compression Tester

This is a compression tester, it's fitted in the plug hole using the adaptor. The engine is cranked over and a reading of how much compression the cylinder makes is captured on the gauge.

A low reading can be caused by a simple fault such as a sticking valve. Picture links to Amazon.com

Leak-down Tester

The OTc is quality kit and will last many years of use. A leak-down tester will require compressed air. The tester measures how much air escapes a cylinder and helps you find weak rings, valves head gaskets etc. Picture links to Amazon.com

Impact Wrench

I love DeWalt, they're make quality tools. This heavy duty but lightweight 1/2 inch impact wrench makes short work of stubborn bolts like flywheel nuts and rusty blade fasteners. Upto 700 ft lbs of torque on tap, I keep one in the trunk of our family car, makes a flat almost enjoyable. Picture links to Amazon.com

Drill/Screw Gun

I use a Dewalt screw gun (also a drill) in the workshop to speed up the process of removing engine covers, carburetor bolts, Armature bolts etc. It's a brushless motor and as tough as nails, I driven over it a few times - still works great! Batteries are interchangeable and so if you have a Dewalt product already you won't need the battery. Picture links to Amazon.com

Torque Wrench

Teng 1/2 Torque wrench, fantastic tool I use it every day and mine is still going strong. A torque wrench is advised for tightening components such as flywheel nuts and blades. The torque spec of these components is very important. Picture links to Amazon.com

If you are considering buying a torque wrench, definitely check out my review of Teng torque wrench.

Briggs & Stratton

This is a popular Hooai Carburettor fitted to walk behind mowers with Quantum engines, but check the engine codes listed. This is an Auto choke carburettor.

This carburettor has a fuel feed bolt in the base of the bowl, dirt in the bolt feed hole is a common issue. Picture links to Amazon.com

Briggs & Stratton

This is a after market replacement carburettor for the Briggs 4-7hp engines. This is the primer bulb style carburettor.

This carburettor has a fuel feed bolt in the base of the bowl, dirt in the bolt feed hole is a common issue.

It comes with a replacement air filter/primer bulb housing gasket. Without this gasket your primer bulb won't work. Picture links to Amazon.com

Briggs & Stratton

This is an original Briggs carburettor fitted to walk behind mowers. Part # 593261, these guy's are made from plastic and I see lots of issues with them. The jet holes are particularly tiny and block so easily. There are a few different types and all look alike, so use part numbers to check before ordering. Picture links to Amazon.com

Briggs & Stratton

This is a popular carburettor fitted to the classic range of Briggs and Stratton engines. This engine is fitted to many different walk behind lawn mower mower models like, MTD, TORO, Murray, Poulan, Craftsman and many more. Picture links to Amazon.com

Honda GCV 160

This is a Hooai carburettor fitted to the Honda GCV160 engine only, not the GVC190. It comes with gaskets, plug, filter and fuel line.

Fitting isn't difficult, just a little tedious, take your time and some pictures of where the old gaskets are positioned and their orientation. Picture links to Amazon.com

Honda GCV 190

This is a Hipa GCV 190 carburettor fitted to the Honda GCV190 engine only, not the GVC160. It comes with gaskets, plug, filter and fuel line.

Fitting isn't difficult, just a little tedious, take your time and some pictures of where the old gaskets are positioned and their orientation. Picture links to Amazon.com

Piston Stop Tool

Universal piston stop tool 10mm and 14mm, used to lock the crankshaft when removing and tightening the flywheel nut. Picture links to Amazon.com
John Cunningham
Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.