There are three main ingredients an engine must have to run (Ignition, Fuel, and Compression). One of the 3 is at fault, and in these videos, we’ll find out which one. 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.
You’ll find useful resources on this page, tips, and links to tools, parts, and supplies required to complete your repair. My mower won’t start 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. It’s a common issue and is covered in these videos.
By the end of these videos, you’ll be a pro!
Common No Start Causes
Before we get knee-deep in sockets and wrenches, let’s take a couple of minutes and check the easy-to-check stuff, you know, the obvious, it’s often overlooked. Sometimes the simple answer is the correct solution. Check out the common no-start causes video below. It covers all the low-hanging fruit and might just save us a bunch of time, and who couldn’t do with more time, right?
Before working on your mower, be sure to remove the plug wire to prevent accidental starting, see “Repair Safety Video”.
If this video didn’t help you any, dig deep and keep moving down the page. The solution to most no-start mower problems is here.
1 Ignition System Section
This video walks you through the process of checking your spark plug with and without a test tool. It also covers plug diagnosis and what each plug condition means. This video works for all mowers.
The 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 the armature, and setting the air gap. This video works for all mowers.
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 the flywheel, removing the flywheel, fitting the shear key, and torquing the flywheel. See Repair Tools on how to use a torque wrench or check out the video here, “How to set a torque wrench video”. This video works for all mowers.
2 Fuel System Section
Gas Shot Test
This video shares a simple hack an old mechanic taught me. It’s excellent for quickly diagnosing carburetor issues. This cool trick works for all mowers and on any gas-powered engine.
The video walks you through the process of identifying your choke type, testing it, and performing common repairs. This video works for all mowers.
Carb Gas Bowl Drain & 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 and clean the gas bowl, fuel jet, and siphon stale gas from the gas tank. This video works for all mowers.
A clogged carburetor is such a common issue, especially after 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.
3 Compression System Section
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 mean.
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.
Briggs & Stratton – Most models take from empty .65 US quarts (.6 lt) 5W30 engine oil.
Honda engines – Most take from empty .58 US quarts (.55 lt) of 10W30 engine oil.
Kawasaki engines – Most take from empty .6 US quarts (.6 lt) 10W30 engine oil.
Kohler engines – Most take from empty .6 US quarts (.6 lt) 10W30 engine oil.
For exact specs, see:
Briggs & Stratton walk behind mower
Briggs & Stratton tractor engine
Tools & Parts
To nail this procedure, you may need the following tools, parts, and supplies.
This is first on the list for a 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 types 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, and stops gas from flowing all over the shop. However, most engines won’t have one. These useful clamps squeeze the fuel line and prevent a spill while you perform surgery—picture links to Amazon.com.
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.
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.
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. A stabilizer will save you money and stress in the long run—picture links to Amazon.com.
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.
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 every day. I have the previous model to this, and it’s still doing its job—picture links to Amazon.com.
Now, this tool is a must-have if you’re removing the flywheel. Why would you want to remove the flywheel? Sometimes the flywheel key shears, it stops your engine from 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
They are used to cut threads. Many flywheels are not threaded, which is 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.
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.
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 in your spark plug; a simple, effective tool—picture links to Amazon.com.
This is a compression tester. It’s fitted in the plug hole using the adaptor. The engine is cranked over, and reading 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.
The OTc is a 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.
I love DeWalt. They 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. Up to 700 ft-lbs of torque on tap, I keep one in the trunk of our family car, which makes a flat almost enjoyable—picture links to Amazon.com.
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 drove over it a few times – it still works great! Batteries are interchangeable, so if you have a DeWalt product already, you won’t need the battery. Picture links to Amazon.com.
Teng 1/2 Torque wrench is a 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 Carburetor fitted to walk behind mowers with Quantum engines, but check the engine codes listed. This is an Auto choke carburetor. This carburetor 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 an after-market replacement carburetor for the Briggs 4-7hp engines. This is the primer bulb-style carburetor. This carburetor 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 carburetor fitted to walk behind mowers. Part # 593261, these guys 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 carburetor fitted to the classic range of Briggs and Stratton engines. This engine is fitted to many different walk-behind lawn mower models like MTD, TORO, Murray, Poulan, Craftsman, and many more. Picture links to Amazon.com.
Honda GCV 160
This is a Hooai carburetor fitted to the Honda GCV160 engine only, not the GVC190. It comes with gaskets, plugs, filters, and fuel lines. Fitting isn’t difficult, just a little tedious. Take your time and take 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 carburetor fitted to the Honda GCV190 engine only, not the GVC160. It comes with gaskets, plugs, filters, and a 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.
- About the Author
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John Cunningham is an Automotive Technician and writer at Lawnmowerfixed.com.
He’s been a mechanic for over twenty-five years and shares his know-how and hands-on experience in our DIY repair guides.
Johns’s fluff-free How-to guides help homeowners fix lawnmowers, tractor mowers, chainsaws, leaf blowers, power washers, generators, snow blowers, and more.