Outboard Motor Starting Problems

Outboard won't start? - Here are 10 Tips to bring it to life


troubleshooting an outboard with starting problems.jpg
troubleshooting an outboard with starting problems
This article describes the most common outboard starting problems and introduces a methodical approach to testing each with simple tools and a basic process.

Outboard Motors need three things

  1. The presense of fuel/petrol/gas being delivered in right mix
  2. Compression in the combusion chamber
  3. A source of correctly timed ignition 

An issue with any one of these three things or the presence of any environment inhibitors, e.g. water ingress will mean a dificult to start or more likely non-starting engine.

Here's our guide to the Top 10 things to check if your engine wont spark to life.

Side note - Unsure of a term in this article? - see our definitions guide)

1. Check the Kill Switch

Most outboards come equiped with a kill cord or key (aka a “deadman”) which when disconnected removes power to the ignition system and thereby immediately killing the engine. One smaller outboards this is a lanyard style cord that attaches to the outboad faceplate (and then around your wrist) but on larger setups with remote controls its often key based. Whichever type you have the effect is the same, removal of the engines ability to ignite fuel.

Make sure the key or cord is attached properly to the motor. Don’t just eyeball it either - give it a wiggle as even if it's just a tiny bit out of place or loose it will prevent it from starting.  Try removing it and put it back into place.

Missing, loose or malfunction kill switches is one of the most common causes of outboards failing to start!

2. Low or Stale/Contaminated Fuel

Checking you have gas is both quick and simple. More likely the problem lies in the fuel supply from tank to the carburettor and on to the combustion chamber or the fuel itself is bad. Once you've checked you actually have fuel in the tank the next step is to checking the fuel supply system and all it's components.

Fuel Supply - Tank Vent & Isolation Tap & Fuel Lines

The first step in checking the fuel supply system is to check that the tank vent and isolation tap are both open. These are usually closed after use to prevent polluting fumes escating when in storage and to stop the flow of fuel to the engine respectively.  The isolation tap are usually located on one side at the base of the main cowling and are 'inline' meaning the tap is open when it is aligned to the direction of the fuel line.  These isolation switches are easy to bump and nudge into the wrong position when the motor is removed or put back on the boat, or even when the motor is tilted up and down.

If you're using an external fuel tank and have recently connected it up after filling the tank ensure you sufficiently prime the tank supply hose give giving atleast half a dozen good gos on the squeeze bulb to ensure all air has been expelled from the host connecting the extenal tank to the outboard.

Having checked these elements the next step would be to check the fuel lines ensuring they are not crimped or damaged in any way. Assuming they are not and you have good supply flow then it't time to check the fuel filter, making sure it is clean and not clogged with substantial particulates.

If all these supply elements seem fine then the final step in the fuel supply system would be to check the carburettor which is responsible for supplying the correct fuel to air mix into the combustion chamber. It's worth mentioning though that it's unusaul that a carburettor would just go out of adjustement and need to be adjusted. If you have recently dropped of banged the outboard or maybe recently had a service then carburettor mix adjustment might be to blame.

Dealing with Contaminated Fuel

Gasoline looses it's potency over time. The exact speed at which this happens varies of the type and rating of the fuel, the environmental conditions in which it is being stored and in what container, e.g external fuel tank, drum, sat in the carburettor float chamber but effect is the same, becoming stale.

Most outboard manufacturers including Johnson, Yamaha, Mercury, Mariner etc recommend their engines are drained of any fuel before any prolonged period of not being used, and definitely when overwintering.


In Neutral?

Many outboards won’t start in gear and it’s easy to accidentally knock the gear shift into forward or reverse. Make sure you’re in neutral!


If you have an electric-start motor, it may be that the battery is low or dead. If it’s a small HP (20 or under, possibly larger), it probably has a pull start as well and you can start it that way. As a teenager, I pull-started a 50 HP, and I’ve seen athletic men who could pull-start an 85. For most of us, the upper limit of pull-starting is more like 20 or 30 HP. Even if you’re not strong enough to pull-start yours, a passer-by might be so it’s a good thing to know where the emergency cord is and what the procedure is.


Two things to check when the motor sounds like it’s almost starting:


Try to start it both with and without using the choke, regardless of what the standard starting procedure is. I find this will often start it when the motor sounds like it’s almost — but not quite — starting.


Try varying the throttle position a little. Sometimes giving it a little more or less gas will help — I don’t know why, but it’s been the case with every outboard I’ve ever used.


If your outboard has an external gas tank, there can be a number of problems between it and the motor. Do a quick visual inspection from the tank to the motor and then run your hand along the fuel hose. Many times, the problem will be very apparent when you do this.



Wrap up

The vast majority of starting problems do not require any specialist knowledge to find and fix, at least to a level enough to get you home where you can employ the services of a professional. An outboard that doesn't start reliably when you might most need it could be asking for trouble.


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