Mower blowing black smoke

This video walks you through the process of diagnosing the route cause of your mowers black smoke.

Over View

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

Lawn mower carburetor problems are common. Black smoke is usually caused by a blocked air filter or sticking choke but a faulty carburetor is also on the list. The faulty carb supplies too much gas which causes black smoke and poor running.

Carburetors aren’t expensive or difficult to fit, if your carburetor is old, go ahead and swap it out. Wow, you’ll really notice the difference.

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

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. Works great on sticking choke cables and levers. 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

Briggs Type air filter

Common pleated paper air filter fitted to Briggs & Stratton engines. Picture links to Amazon.com

Honda Type air filter

Common paper pleated air filter fitted to Honda mowers and Honda engines fitted to branded mowers. 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

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

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
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.