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Frequently Asked Questions

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Engine Won't Start

Why won't my engine start?

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 compression.


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 enhancements.

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.

Carburetor Cleaning Recommendations
  1. Disassemble carburetor.

  2. Remove all old gaskets, seals and sealing material.

  3. Use commercial carburetor cleaning solvents (such as Briggs & Stratton carburetor cleaner to clean carburetor parts and body.

  4. 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 cleaner bath.

  5. 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
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 PDF.

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 Authorized Dealer.

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 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.

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