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Tohatsu troubles

9K views 56 replies 21 participants last post by  cthoops 
#1 ·
We have a 2010 Tohatsu 9.8 hp outboard on our boat. The previous owner said it could be temperamental.

It ran pretty well for the first six weeks or so, but now it either runs very smoothly, or it's very rough and acts like it wants to stall (and occasionally does). When it's running rough, increasing/decreasing the throttle or fiddling with the choke doesn't help it. Yesterday we went to the dock to get water, etc. and it purred right along. On the way back, it stuttered away (made for a stressful return to the mooring).

Before the season we put in a new water/fuel separator filter, we always run it dry, and we use high octane fuel and put stabilizer in it. We top off the tank frequently (it's an external 3+ gallon tank), and it gets used once a week.

At this point we're not comfortable heading out for a sail until we get it straightened out. Any thoughts? Would it be something that we can try to fix ourselves? Mr. Cthoops was an airframes mechanic 30 years ago in the Marines and he can fix any bicycle, but he doesn't consider himself a motor head. I'm really good at cheering him on and handing him things.

Any suggestions would be greatly appreciated. Thanks.
 
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#33 ·
One more point (been resisting do to not wanting to jinx myself) is that I don't follow any recommendations that I probably should. I don't use a stabilizer, I don't shut off the fuel valve and run it till it dies, I don't run ethanol free gas...hell I don't even winterize it. One thing I do though is run the boat year round, which I think solves a lot of problems. At least a couple times a month throughout winter. If I lived in the cold country I would definately be more pro-active with preventive maintenance. Anyhow...it starts on first pull every time. I love my Nissan / Tohatsu outboard. Geez...I hope I didn't jinx myself.
 
#34 ·
One more point (been resisting do to not wanting to jinx myself) is that I don't follow any recommendations that I probably should. I don't use a stabilizer, I don't shut off the fuel valve and run it till it dies, I don't run ethanol free gas...hell I don't even winterize it. One thing I do though is run the boat year round, which I think solves a lot of problems. At least a couple times a month throughout winter. If I lived in the cold country I would definitely be more pro-active with preventive maintenance. Anyhow...it starts on first pull every time. I love my Nissan / Tohatsu outboard. Geez...I hope I didn't jinx myself.
Agree, if you use the motor on a regular basis and get good quality fuel and check your filters regularly, you probably won't have any problems. I never used to drain the carb on a number of motorcycles, but I rode all year although not too much in the summer.

As mentioned, the only problem I had was to forget draining the carb on my Honda 2 HP outboard which sat all winter, that one got me. I do use Berryman's fuel additive, which absorbs water, which I understand ethanol fuel absorbs from the air? Not sure if the additive is necessary, but I don't think it hurts anything?

Paul T
 
#37 ·
I have a Tohatsu 6HP 4 stroke with an external tank. When disconnecting the fuel line at the tank I get sprayed with fuel which then runs into the bottom of the boat. "open the vent" you say. I did. It appears the vent only vents incoming air to the tank. After the tank sits in the hot sun with the vent open I get a large whoosh when loosening the filler cap. I don't know if there is a pressure limit before it vents "out" or if the tank would eventually burst?. I am going to see if I can retrofit the cap so it will vent in both directions.

End result is that like the portable gas cans sold in California, I spill more gas than I ever did before.

Paul T
 
#39 ·
I have a Tohatsu 6HP 4 stroke with an external tank. When disconnecting the fuel line at the tank I get sprayed with fuel which then runs into the bottom of the boat. "open the vent" you say. I did. It appears the vent only vents incoming air to the tank. After the tank sits in the hot sun with the vent open I get a large whoosh when loosening the filler cap. I don't know if there is a pressure limit before it vents "out" or if the tank would eventually burst?. I am going to see if I can retrofit the cap so it will vent in both directions.

End result is that like the portable gas cans sold in California, I spill more gas than I ever did before.

Paul T
I have the same exact setup.

Wow, thanks Paul T, it never occurred to me that the valve was one way. My dink and motor have been sitting in the sun all week. I just sent my wife down to the boat to check the gas tank, damn. I should have thought about that.
 
#41 ·
My wife just rescued our Tohatsu gas tank from the sun. She said there was a lot of pressure in it when she loosened the cap. Crap, dogged a bullet on that one, it's always humbling when I realize what an idiot I can be at times. Jeeezzzz. :hammer

It never occurred to me that the valve was one way.
 
#42 ·
I wonder if the tank manufacturers conducted a failure test with the one way vent caps? As far as I could see, there was just the small one way valve in the middle of the cap. The one time I left it in the sun there was a LOT of pressure in the tank.

Has anyone had a tank split or leak because of the excess pressure that can develop?

Paul T
 
#43 ·
Just wanted to post an update.

Today Mr. Cthoops and I removed the carb, sprayed it with carb cleaner (black, dirty stuff was definitely coming out), used a can of air to dry it out, emptied the external fuel tank into the car, put brand new gas into the fuel tank, and added a different carb product to the gas (can't remember the exact name right now, but it's supposed to keep the jets clean). We also changed the spark plug for good measure (the old one was looking kind of dirty).

After putting the carb back in, we crossed our fingers and started it up. It's purring like a kitten. I don't think its sounded this quiet and smooth since we bought the boat in April!

This was the first time either one of us had done anything resembling outboard maintenance, so we are pretty darn proud of ourselves. Everyone was right - it really wasn't that hard. And we didn't drop anything in the water!! Hopefully this will be the last of our outboard issues for the rest of the season.

Thanks everyone for the advice and encouragement.
 
#45 ·
Just wanted to post an update.

Today Mr. Cthoops and I removed the carb, sprayed it with carb cleaner (black, dirty stuff was definitely coming out), used a can of air to dry it out, emptied the external fuel tank into the car, put brand new gas into the fuel tank, and added a different carb product to the gas (can't remember the exact name right now, but it's supposed to keep the jets clean). We also changed the spark plug for good measure (the old one was looking kind of dirty).

After putting the carb back in, we crossed our fingers and started it up. It's purring like a kitten. I don't think its sounded this quiet and smooth since we bought the boat in April!

This was the first time either one of us had done anything resembling outboard maintenance, so we are pretty darn proud of ourselves. Everyone was right - it really wasn't that hard. And we didn't drop anything in the water!! Hopefully this will be the last of our outboard issues for the rest of the season.

Thanks everyone for the advice and encouragement.
Good for you!!, Thanks for the feedback. Suggest you drain the carb if it is going to sit more than a week or two.

Paul T
 
#46 ·
Having 2009 Tohatsu 9.8hp for the last 4 seasons, the only real problem I came across is the upper cylinder having tendency to flood, which subsequently fairly quickly tends to foul the spark plug - I always carry two new with me (they get changed each season regardless of condition). The engine (my experience) does not like any other plugs than the NGK. I have tried once Champion equivalent and Bosch (I was told these were equivalents), and run into a lot of uneven idle, hesitation and poor performance. Do very carefully gap the plugs to specifications - failure (again, my experience) caused poor operation and misfire. I change fuel filter after each season and add fuel stabiliser to the last tank of fuel of the season. I have disassembled carburetor this spring and found it in surprisingly clean condition - bottom line is the fuel quality. Besides that, the motor so far is rock-solid and my fuel usage is about 1.2-1.5l/hr at about 60% throttle.
 
#47 ·
At the risk of jinxing myself, I thought I would post this update so that it might help someone in the future.

We thought that after cleaning the carb and changing the spark plug our troubles were fixed because the outboard idled smoothly on the mooring. Unfortunately when we actually put it in gear and headed out we discovered that while the symptoms had improved somewhat, the engine still wasn't happy.

Someone on this forum had suggested it was likely either the carb or the fuel lines, so we replaced the lines running from the external fuel tank to the outboard (including the lines leading to and from the separator filter), and this included a new primer bulb. I'm thinking perhaps the PO had used the lines from the previous, smaller outboard because the new ones seemed more robust and "bigger". Regardless, they likely needed to be replaced because when Mr. Cthoops started to remove the old line from the separator filter, it immediately split in half.

Anyway, I don't know if the lines weren't large enough or there was gunk that had built up in them, but the bottom line is we've taken the boat out twice since replacing all of this and the outboard has truly never sounded better. It's quieter and runs ever-so-smooth. I am SO relieved!

Thanks again for the advice, everyone.
 
#55 ·
It was likely the old gas that was still in the fuel line.

Regards,
Brad
 
#50 ·
Just as a side note, Tohatsu is the manufacturer of all small outboards. They build them and badge them as Suzuki, Mercury, Evinrude etc. Kepp your fuel clean and run them periodically. I dont drain the bowl or let it run dry and I also use alcohol free fuel with stabilizer.
 
#51 ·
That's not quite accurate. Tohatsu make many small outboards, but not all. They make the small Mercurys, Nissans, and of course Tohatsus, but they don't make Honda, Yamaha, and Suzuki. Not sure about Evinrude.

Letting it run dry or draining the bowl is the single most important thing you can do to keep an outboard running nicely.
 
#52 ·
In my snowblower, generator, and various outboards, running it dry still leaves a small amount of fuel in the bowl. Draining gets virtually all of it out. I forgot to drain one season and paid the price the following spring. Spent several hours fixing it, 2 HP Honda, had to take the tank off to get the carb off.

Paul T
 
#53 ·
If you suspect the fuel is the problem here is a quick easy way to check it. It will take about 15 minutes to do so.
First disconnect the fuel line from the carb and drain some fuel into a container, I prefer to use a glass jar, about a 1/2 to a cup is all that you need to drain. Then set that aside and let it set without being agitated. After the fuel has set then look at the bottom of the jar from the top. If there is water in the fuel you will be able to see it.
If there is not water in the fuel, tip the tank so you can look in the fuel fill cap and let it set for a bit and see if there is water in it, water will always go to the lowest point so make sure you are looking in the corner and it is the lowest point, prop the tank up if you need to.
when you have ruled out the water in the fuel, the next step is to clean the jet at the bottom of the fuel bowl. First drain the bowl and then remove it, at the bottom of the lowest part of the pickup is a brass piece, use a flat tipped screwdriver to remove it and check to see if it is clear. I will generally run a small wire through it just to be sure and shoot some carb clearer through it. Even a small piece of debris or dirt will make the engine run rough or not even start.
I use a 3.5 tohatsu engine on my dinghy and have had the same problems as described and this is what I have found the problem to be.
Also I use just regular fuel from the gas station the 87 octane type that has ethanol in it. I have found that it works fine but it does take a toll on the fuel line after about a year so I replace it. I do not put any additives in the fuel, the trick is to use the fuel with in a 6 month or less period.
Hopefully this will help in solving your problem, fair winds and the best of sailing to you.
 
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