As a professional fly fishing guide, I spend a lot of time on the river. During the past year, most of that time has been in my river boat, due to our seemingly never ending high water conditions. When on the river, it is vital that my engine is operating at the peak of performance, particularly in high water. Recently I have encountered some problems with my outboard motor.


It would start fine, but when I put it in gear and revved it up, it balked and sputtered. It would eventually get under way but not at maximum output. I had a dilemma. I was in the first day of a two day guide trip. I only have one boat and motor and it was not operating at one hundred percent. I needed to put the motor in the shop but I needed to finish my trip. I somehow managed to finish the day. Luckily the trout were cooperating and we had a good day fishing. That night, at the lodge, I discussed my motor woes with my colleagues. I heard a few opinions but the consensus there seemed to be spark plugs. I pulled the plugs and they looked okay.


The next day I returned to the river to finish the trip and my motor really started acting up. I limped back to the ramp and borrowed a motor from Gary Flippin at Rim Shoals Trout Dock. I was able to finish the day. Once again we were able to boat plenty of fish but I was a nervous wreck from hassling with the engine.


The next day I was at Bearskin Marine as soon as it opened. I explained to Floyd what was happening and he went to work. I picked up the motor the next day. Floyd said the motor looked pretty good and the spark plugs showed little wear. We discussed the engine problem and he suggested that the problem could be the fuel that I was using.


A number of our local gas stations had begun carrying gasoline that contained approximately ten percent ethanol. Ethanol has several qualities that make it a poor fuel for outboard motors. It attracts water. Since outboard motors do not have sealed fuel systems they can take on water if ethanol is used. Water and gasoline don’t mix. The water settles to the bottom of the tank where it enters the intake tube and goes into the motor. You can imagine the results.


Ethanol is also a powerful solvent. As we walked through Floyd’s shop, he showed me several fuel lines that had been put out of commission by the use of ethanol. One fuel line was inoperable because the ethanol had dissolved the glue connecting the intake tube to the line itself. This allowed air in the fuel line which severely hampered operation. Another intake tube had stretched and when the owner had pushed it into the fuel tank bending the now too long tube and crimping it in the process. This cut off the fuel supply to the engine.


I had been trying to use pure gas but often for convenience sake I would fill up at my local gas station that carries fuel with ten percent ethanol. On at least one occasion, I had stopped at one of the area stations that advertises that they carry pure gas only to find out that they had been delivered fuel that contained ethanol. I was short on time and I filled up any way. It was a bad idea.


I put my motor back on my boat and filled my gas tank with fresh pure gasoline. I took it to the river and launched. My motor was running better but it was still not up to par. I was concerned. Once again I discussed the problem with my colleagues. Gary Flipin suggested using high octane gasoline. Gary maintains several rental boats and he said that he had experienced the same problem and had switched to high octane (93) pure gasoline and the problem had gone away.


The next time that I filled my tank I bought high octane pure gasoline. The improvement was instantaneous. My engine is now running at peak performance and I am much more confident in its general operation.


I have since learned that there are additives (made by Stabil) that you can add to fuels containing ethanol that will overcome its problems and help the engine run properly. They are available locally and cost about twenty dollars for enough additive to treat three hundred and twenty gallons. I have not tried any of them. I will take a more conservative approach and will try to only run pure high octane gasoline in my motor from now on. I think that I will also buy a bottle of the additive to use if I get stuck with some ethanol fuel.


If you are experiencing any problems with your outboard motor check the fuel that you are using. A change to better fuel may cure your problems.




  1. Mr Berry,

    I have a newer Mercury 50 HP two cycle outboard. The last few trips the motor cannot hit 5500 rpms due to ethanol. I have drained tank dry and put BP 93 octane in the tank. Others should avoid ethanol gas. I feel like my motor may be ruined . The motor bogs down and just won’t run ./

  2. You readers may be interested in this very easy and cheap fix for their older ethanol plagued outboard motors using Marvel Mystery Oil

Leave a Reply