Safety procedures reduce the possibility or accidents and injuries when working
on small engines. Before working on your engine, please read our Small Engine Operation
Safety FAQ. Generally, an engine requires three things to start - fuel, spark and
The most common reason an engine will not start is due to an interruption in fuel
delivery to the combustion chamber, usually caused by a restriction in the carburetor.
Often, the restriction is caused by stale fuel , or dirt and debris.
Carburetor problems are almost always caused by dirt particles, varnish (stale,
old fuel)and other deposits that block the narrow fuel and air passages inside.
Gaskets and O-rings are also common sources of problems. Over time they shrink,
causing fuel and air leaks that lead to poor engine performance and eventually the
engine fails to start at all.
The design of your carburetor depends on the size of the engine and the application.
Engines designed for lawn tractors require a precisely tuned carburetor with a choke
and idle mixture system. Walk-behind mower engines operate well without these design
For a typical example of how an engine may sound when it stalls due to lack of fuel
flow, please listen to the following:
Before Removal of Carburetor
When removing the fuel hose (if equipped) from the carburetor on a machine without
a fuel shut-off, drain any fuel from the tank first. Do not thread a bolt or cap
screw in the removed hose end. Screw threads will damage the hose ID and rubber
particles will enter the fuel system. Note position of governor springs, governor
link, remote control or other attachments to facilitate re assembly. Do not bend
links or stretch springs.
Remove all old gaskets, seals and sealing material.
Use commercial carburetor cleaning solvents (such as Briggs & Stratton carburetor
cleaner to clean carburetor parts and body.
When cleaning non-metallic parts (plastic, nylon Minlon, etc.) do not leave in commercial
carburetor cleaner bath more than 15 minutes. NOTE: Parts containing rubber, such
as seals, O-rings, or pump diaphragms should never be placed in commercial carburetor
Use only compressed air (blowing in both directions) to clean out all openings and
passages. NOTE: Do not use wires, drills or any other devices to clean out metering
holes or passages.
Make sure the fuel itself is fresh and of the correct type. We recommend the use
of clean, fresh, lead-free gasoline with a minimum of 87 octane / 87 AKI (91 RON)
is used in our engines. For altitudes above 5,000 feet (1524 meters), a minimum
85 octane / 85 AKI (89 RON) gasoline is acceptable. We also recommend gasoline be
purchased in small quantities, not more than a 30 day supply. Fresh gasoline minimizes
gum deposits, and also will ensure fuel volatility tailored for the season in which
the engine will be operated. Please visit our for tips on handling gasoline.
Also remember a clogged or dirty air filter restricts the amount of air flow to
the carburetor. This will cause a rich fuel/air mixture that can flood the engine,
or cut the air supply enough that engine will not run. Single-element air cleaners
should be replaced every 25 hours (or once a season). In a dual-element system,
the pre-cleaner should be replaced every 25 hours. If the engine is operated in
especially dusty conditions, the filters may need to be changed more frequently.
Lack of spark is another common reason an engine will not start. Today's small engines
contain a solid-state ignition armature mounted adjacent to the flywheel. The only
moving parts in the system are the magnets mounted in the flywheel, which interact
with the armature to produce electrical current. The majority of ignition armatures
are designed to be replaced, not repaired, if they fail. Most engines built through
the early 1980s contain a set of mechanical points, known as breaker points, under
the flywheel. The points open and close an electrical circuit required for ignition.
Before you replace a suspect ignition armature, always test the ignition with a
spark tester (service part number 19368).
Keep in mind that most engines contain one or more stop switches wired between the
engine's ignition system and equipment components. You can trigger such a switch
by releasing the brake bail or removing the grass discharge unit on a lawnmower,
or by standing up from the seat of a lawn tractor, triggering a switch under the
seat. These switches cut power to the engine by grounding one of the copper windings
in the ignition armature. Also check for faulty electrical switches such as oil
safety shut-down, and a tractor's seat and mower deck safety switches.
If spark does not occur look for -
- Improperly operating interlock system
- Sheared flywheel key (breaker points only)
- Incorrect breaker point gap (when so equipped)
- Dirty or burned breaker points (when so equipped)
- Breaker plunger stuck or worn (when so equipped)
- Shorted ground wire (when so equipped)
- Shorted stop switch (when so equipped)
- Condenser failure (breaker points only)
- Incorrect armature air gap
- Armature failure
- Worn cam bearings and/or camshaft (breaker points only)
Inadequate compression, perhaps due to improper valve clearance or a sticking valve,
will also prevent your engine from starting. If a compression component such as
an exhaust valve leaks during the compression process, there is a decrease in the
overall pressure of the charge and a dilution in the concentration of the charge
by maverick air. Maverick air is undesirable, unaccounted for air entering the engine
through leaks cause by worn, loose, or failed engine components. An exhaust valve
leak can result in maverick air entering the combustion chamber through the muffler.
For additional information regarding a no-start condition or poor engine performance,
please visit the Troubleshooting section of our website or download our Troubleshooting
By viewing your engine model's Illustrated Parts List (IPL) you can obtain any engine
part numbers you may require. With your engine numbers, please visit our Illustrated
Parts List look-up page and enter your Model and Type numbers into the Search Fields
located near the top of the page.
The numbers listed next to the part illustrations in our IPLs are called Reference
Numbers. These numbers are one to four digits in length depending on the part. The
Reference Number is used to locate the specific Service Part Number (usually six
digits) you will require for ordering purposes. Most of the IPLs will require that
you scroll down past the part illustrations to the pages where the Service Part
Numbers are located. The Service Part Numbers are listed in numerical order according
to Reference Number.
To purchase parts online, visit our website's Genuine Parts section. This area of
our site contains all the engine parts (starter motor, crankshaft, piston, etc.)
that are sold directly from Briggs & Stratton.
Parts can also be ordered via phone by calling (800) 444-7774.
A good source for engine specifications and technical servicing information would
be a Briggs & Stratton Repair Manual. Please visit our Learning Resources page
and enter the Model and Type numbers into the search fields located near the top
of the page to view the products available for your engine.
To best determine cause of failure, please consult a local Briggs & Stratton
Your Briggs & Stratton Authorized Dealer has all the information relating to
Briggs & Stratton warranty information, replacement engines, short blocks, parts,
pricing, service/repair, specifications, etc.
For your convenience, we offer three easy ways to locate your nearest Briggs &
Stratton Authorized Dealers:
Use our website's Service Center Locator.
Visit www.yellowpages.com and enter "Lawn Mowers" or "Engines-Gasoline" in the Category
search field and your Postal Code in the Location search field.
Call the Briggs & Stratton Automated Hotline at (800) 444-7774. This hotline
is available 24 hours a day/7 days a week and features voice recognition technology
to assist you in finding the Briggs & Stratton Authorized Dealers in your area.
Automated maintenance tips, product information, and FAQs are also offered through
voice activated menus.
Please read and abide by any applicable Safety Information contained in your engine
Operator's Manual. The material provided above is not intended to replace work performed
by a Briggs & Stratton Authorized Dealer. Terms and Conditions apply to all
of the information presented on this website. Always be sure to completely read
and understand your engine Operator's Manual.