Skip Navigation

Select Language

Diagnostic Center

What Should I Do When My Marine Engine Won't Start?


Whether you have a fishing boat with an outboard motor or a speed boat with an inboard motor, you count on the motor to start every time you engage it. Nothing ends a day of fun on the water quicker than hitting the start button or pulling the start cord and hearing your boat engine grind and grind without the slightest indication of starting. A hard starting engine is an indication of a problem that needs to be resolved right away before it leaves you and your passengers stranded on the water.

Person navigating their boat in the open water.


Like any gas-powered engine, your marine engine needs three things to start and run properly:

  • Air
  • Fuel
  • Spark to ignite the air/fuel mixture

If any of these necessary elements aren’t supplied at the proper time and in the proper amount, the engine won’t start.


While most starting issues are related to air or fuel supply and the spark, there are some other problems that can cause your boat engine not to start:

Flame Arrestor/Air Box icon.

Clogged Flame Arrestor/Air Box

Designed to stop flames from coming in contact with other fuel, flame arrestors help prevent a fire from breaking out. These devices can become clogged with carbon and debris, which will negatively affect the air/fuel mixture, resulting in no start/run rich situations. Remove the clogged flame arrestors and remove the debris using carb cleaner and a wire brush. Air boxes, especially those that are stored in non-marine environments, are susceptible to being clogged with debris such as animal nesting. Make sure the air box is free from debris prior to each startup.

Fuel filter icon.

Dirty or Clogged Fuel Filter

The fuel filter keeps dirt in the fuel from getting into the carburetor, and like the air filter, may eventually become clogged and prevent a sufficient amount of fuel from passing into the combustion chamber, preventing your engine from starting.

Spark plug icon.

Faulty Spark Plug

A spark plug fouled by fuel, carbon, dirt or oil on the electrodes may not produce a spark strong enough to ignite the air/fuel mixture and start your engine in older two-stroke engines. Over time, deposits can build up on the spark plug’s center and side electrodes. This changes the gap of the spark plug and can short-circuit the electricity before it reaches the center electrode tip, weakening the spark.

Battery icon.

Dead Battery

Leaving the radio, lights and pump on while anchored can run down your boat’s battery. If your boat has a two-battery system, forgetting to switch the battery before playing the radio or other accessories can run down both the house battery as well as the starting battery.

Gas pump icon.

Old Gas

Ethanol-based gas can go stale in 30 days or less. Make sure the fuel tank contains fresh fuel, is properly connected and vented and there are no kinks or breaks in the fuel line.

Engine icon.

Engine Not Primed

Make sure the engine is primed with fuel and choked properly at start if necessary.

Spark plug wires icon.

Loose Spark Plug Wires

Improperly connected spark plug wires can make starting your engine difficult. Make certain all spark plug wires are properly connected and free of breaks. Also, check that the distributor cap and rotor are functioning properly.

Kill switch icon.

Problems with Kill Switch

Check that the safety lanyard/kill switch is functioning properly and in the correct position.


Green check mark icon.

Clean flame arrestor/air box.

Green check mark icon.

Replace dirty or clogged fuel filter.

Green check mark icon.

Replace fouled or dirty spark plug.

Green check mark icon.

Switch to house battery when anchored and carry a jump starter.

Green check mark icon.

Replace old gas with fresh gas (properly dispose of old gas).

Green check mark icon.

Replace loose or damaged spark plug wires.

Green check mark icon.

Test the kill switch to ensure its working and in the correct position.

If none of these suggestions resolves your starting issues, then it’s time to call on a professional mechanic who specializes in small engines.

Boat engine opened up.

Did You Know…

Q: Why don’t marine engines have air filters
A: Since they operate in a mostly dust-free environment, marine engines typically will not have an air filter. Outboard motors utilize an air box in front of the carburetors to quiet the sound of air intake to the engine. Inboard motors use a flame arrestor on their carburetors to eliminate the possibility of fire and/or bilge explosion.

Learn more about marine spark plugs and marine batteries, find your part, or find where to buy your part today.

The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

Related Stories

Related Parts

Champion® offers a wide variety of products for all your automotive needs.
Check them out!