Outboard motor problems? It’s the gas, stupid! (ITGS!) Well, maybe..

Here’s a story about a very minor boating disaster that I experieced while fishing on my favorite Minnesota lake in Scott County. The problem and the solution is probably “old hat” to veteran boaters, but it was a new thing for me. Perhaps this has happened to you.

mariner 15 outboard motor

About two weeks ago, I decided to try out a little fishing boat I purchased from my neighbor. It’s just a little 14 footer with an old 15 hp Mariner outboard motor of uncertain age (see photo.) I filled it up with the typical mixture of regular unleaded gas from Qwik Trip and two-stroke motor oil at a ratio of 50:1. After nearly dislocating my shoulder from pulling on the starter cord, and applying a little choke, it finally started up with a small blue cloud of smoke. It ran like a top.

With my four year old daugher along for good luck, we chugged along quite nicely, and things were looking up. While turning around sharply, I cavitated the boat (got to much air under it around the prop) and the engine revved up very briefly and quit. Back to pulling on the rope again. It fired… putt putt putt… then quit. Again… putt putt putt.. then quit. Seemed like a fuel problem to me. More pulling… the motor would always fire, but would not keep running.

great blue heron in scott county mn lake
Stranded on my favorite (undisclosed) Minnesota lake! This Great Blue Heron must be laughing at me. Looks like a photo from Jack Handey’s “Deep Thoughts.”

A nice guy with a jet ski saw my predicament and pulled me to shore. A friendly fellow standing on the dock had been observing all of this while puffing on a cigarette. He stated he had a similar problem with an older motor on his pontoon boat. His diagnosis: “It’s your oxygenated gas!”

“Say what?”

“Yeah, its your gas. Did you buy it at Holiday, or SA, or someplace like that?”

“Well, yeah?”

“Most of the gasoline sold today has at least some alcohol in it. Your old-style carburetor can’t handle it. It fills up with some kind of gel and messes up the float.”

I stood there looking like a calf at a new gate.

“Yeah,” he continued. “You gotta go down to Fleet Farm (Lakeville) and fill up a five gallon can with non-oxygenated gas. And they won’t just let you fill up your car with it either. You gotta bring a can. Then change out your spark plugs and replace the gas. That will probably do the trick.”

This sounded a lot better to me than paying a boat mechanic $119/hour plus parts to fix it. I switched out the gasoline with my new mixture of non-oxygenated fuel and oil.

old 15 hp outboard with cover off of it.

So, what’s the deal with oxygenated fuel? Turns out that oxygenated fuel leans out the air/fuel mixtures in carburetors. The alcohol has a higher heat of vaporization so additional heat is needed to vaporize the fuel. I couldn’t find anyone who knew about the “gel” in the carburetor. However, I did learn from MasterTech Marine that fuels mixed with alcohol do take up water more readily than those with out it. The result can be a phase separation; A mixture of gas and oil will float on top of a layer of water and alcohol.

Why is gasoline oxygenated with alcohol? Alcohol causes less carbon monoxide to be produced by gasoline combustion. This is especially important in cold weather areas and during winter months.

Here is an article about non oxygenated gas, along with a list of places where you can find it in Minnesota.

So I switched out the gasoline with the new mixture of non-oxygenated gas and oil (50:1) but did not bother with the spark plugs. I pull the cord and it starts right up (way easier than before) but then it quits after a few seconds. More pulling. More putting. It fired up nicely, but it still seemed like it wasn’t getting fuel, so it would cut out. More pulling. I said some bad words. But this time I was smart- I had some oars with me so I could get back to the dock!

I pulled the motor back out, brought it to the neighbor I bought it from, and then he gave it to his brother-in-law to fix. The diagnosis and cure was swift; the plugs needed to be re-gapped!
The motor goes back on the boat and the boat goes back in the lake. One small pull…VROOM! The motor ran like crazy… better than ever…

So now I am thinking it was just the spark plug gap issue, but now the motor runs so well, that I am certain the gas was at fault. But the carburetor seems ok. To get me even more confused, a friend of mine is telling me that I just need to use plain old premium gas from SA or Holiday, it will be fine. It’s just an octane issue? Now I think I don’t know anything.

Anyone out there know anything about boats and gas? In the meantime, I’ll stick with the new gas mixture.

Minnesota lake shore and lake front homes for sale.


Comments (6)

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  1. Joe says:

    You are right on about the gas. I have an 88 johnson 30 hp. worked great at cabin every year with normal winterizing. We (she) sold cabin to invest in future??? anyways, within one year my motor began to bog down in the lake…not the driveway with old barbage can full of water, only in the lake when I would punch it. An old biker down the road saw my frustration and the cans of carb cleaner ect.. He walked up (with his beer) and asked the same question you were asked. “Used gas from Standard (BP) did’t you? I said yea I try to get good gas like gas from Standard. He laughed, took a big swig of his beer and said, It’s that *&&###*$$* alcohol. I looked at his beer and said I totally agree. I quit drinking over 20 years ago. He laughed asked if I can rebuild my carberator myself? I said yes. He said that I needed to go to White Bear Lk. at a parts place (can’t remember the name) and get a carburetor rebuild kit. I called aroud and he was right, only place that had it. Then he told me as he walked back down my driveway, “Don’t ever put that *&&##$@#** gas in anything smaller than your truck!” I rebuilt carb. Only use gas from a Shell station, “Alcohol free just like me.” Never seen the problem again going on three years now. It does cost MORE, but not in the stress/worry/hassle factor.

  2. protaras says:

    i’ve had a lot of problems with my motor..hate it..

  3. richard says:

    my engine starts and runs slow but labors when i speed up,does not quit but only runs slow. I am thinking it could be very old gas. it is a 2004 mercury 25 hp.

  4. g.emahiser says:

    You are on target with the gas issue. In International Falls, we have stations that have non ethanol gas, and people in the know understand the difference… tourists come up there with their O/B engines and think they can use anything that pours. Keeps our repair people busy. Don’t recall hearing many of them being offering good advice on how to avoid it in the future. Hummm. Price of leaving home, I guess.

    Oh, did you REALLY leave the dock without oars? You are bold.

  5. chuck says:

    I just spent over $300 having a carb overhaul on my ATV. When I picked it up from the repair shop…the mechanic said the same thing. STOP using the oxygenated (ethanol) gas. It totally gums up the carbs. His shop has had three times the number of carb overhaul than previous years. His opinion is that gas companies are dumping more than the 10% as per state requirement. And any gas that sits around (ATVs, lawnmowers, outboard motor tanks, etc.) is like putting gelatin into your motors.
    By the way, be prepared for even more problems, the 10% ethanol will be going up to 20% soon. State Legislature threw a bone to the farmers…disregarding the problems that a lot of engines are going to have.

  6. ron says:

    You can get get marine stab at Walmart it cost a lot but 1 oz to 10 gal of gas is all it takes. I have a 78 Johnson 115 that and after getting broke down on the river. I had used the old fuel tank got dirt in filter and the older outboards wikk not run with any dirt. New fuel line I then put a inline filter and now it runs great. I use Costco or zip trip gas and have no problems.

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