Outboard motors – fuel issues

The modern outboard motor is an amazing thing.  In comparison to the outboards I used when I started sailing back in the mid-1970s the new motors are very reliable.  The 4-cycle motor is a lot easier to keep going, especially because there is no need to mix oil into the gas.

I remember one outboard, a small 1HP or 1/2HP thing, that seemed to run on spark plugs.  I swear I never remember it ever running out a full tank of fuel without needing at least one spark plug replacement. I don’t know what my Dad did with that motor as I really only remember it being around for one or two sailing seasons.

At Sage Marine we have multiple outboards for use with the company boats.  In total we have four outboards, three of which are Honda 2HP (aka, BF2’s).  The 2HP is now sold as the 2.3HP (aka, BF2.3).  These motors have been very reliable and power a Moore 24Montgomery 15 and Sage 17.

The usual problem with these motors is the fuel.  Why the fuel?  ETHANOL!

All new outboards will run 10% ethanol blended fuel (aka, E10).  This is the type of blend that is sold at almost every gasoline station in the US.  I don’t intend to discuss yes/no to ethanol … what I will discuss are a few of the known problems:

  • ethanol is a great cleaner.  This causes problems in outboards, and their fuel tanks, as all the gunk is cleaned out of the fuel system and gets into the carburetor.  This results in a couple of issues: float bowl getting ‘gunky’ when fuel evaporates with all the stuff cleaned out the gas tank; carburetor’s fuel jets becoming clogged with the gunk.
  • ethanol attracts water.  In a marine environment this isn’t good as the 100% humidity at water level means there is lots of water molecules in the air for the ethanol to hook up with and foul the gas.

The two things above mean outboard owners need to assure the fuel is in top condition.

  • Some marina’s do sell ethanol free gas.  This is the best solution … though the gas does cost more.  Good thing sailboats don’t burn a lot of gas!
  • Every few weeks, no more than a month, empty unused fuel in the boat’s gas can into your car and get fresh fuel for the outboard.    Another options is to use this ‘old’ fuel in their lawnmower or other motorized lawn & garden tool. WARNING: DON’T do this is your outboard is a 2-cycle motor!
  • Treat any fuel purchased with stabilizers.  Taking suggestion from The Outboard Dr. I treat all fuel with both STA-BIL Marine and Sea Foam.  Yes, both products.

Now here is an area of contention (to be honest this entire topic is full of ‘contentions’) – should your outboard be ‘run dry’ after every use?  Running an outboard dry involves shutting off the fuel feed and allowing it to idle until it uses all the fuel.  For a Honda 2HP this can take 15 or more minutes.

I don’t run the Sage Marine outboards dry.  During the sailing season the motors are run weekly so the fuel in the carburetor doesn’t evaporate.  When the fuel doesn’t evaporate the gunk doesn’t build up in the fuel system. During the late Fall, Winter and early Spring, when the boats are not in the water, I run the motors at least once a month to keep fuel in the carburetor.

How do I do this?  The Honda 2HP, and 2.3HP, are air cooled motors.  Air cooled means there isn’t an impeller moving water through the motor.  This means you can start, VERY VERY VERY VERY carefully, a Honda out of the water.

Couple of words of warning –

  • confirm your Honda 2, or 2.3, isn’t one of the rare water cooled models.
  • start and always stand to the back of the motor.
  • NEVER NEVER NEVER get near the propeller.
  • DO NOT run the motor above idle speeds as without water putting drag on the propeller the engine can over-rev (meaning the RPMs are higher than designed and the motor tears itself apart).


Here is a short video of the outboard motor running I just conducted.

All motors ran for about 3-5 minutes.

Doing the above has kept Sage Marine’s outboard 98% problem free.

– Dave

NOTE: I originally posted this January 2015 on Sage Marine’s BLOG. In a short time the BLOG will be closed – stupidly. I am reposting this information so it is not lost.

3 thoughts on “Outboard motors – fuel issues

  1. When using the outboard to motor sail, the motor will not sit level. Is this a problem for engine lubrication? I try to keep the boat as flat as possible, but it does not take much to move the oil level in the inspection window.


  2. John: the oil indicator outboards are for checking when the motor isn’t running. It is normal not to see any oil at the indicator when the motor is running. For me the point the boat is heeling enough to cavitate the prop I’d worry about oil no longer lubricating the motor. (this means knowing the angle so you know when you have reached the ‘cavitation angle’ when heeling towards the motor.)

    The Honda 2/2.3 is a wet sump and has not pump – think the motor parts splash the oil around and lubricate the motor. Other motors have an oil pump and usually have a low oil pressure alarm.


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