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Old 07-07-2015, 09:41   #16
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Re: Tohatsu 3.5 no power

Correct me if I'm wrong, but I think the high speed jet on that engine is the tapered wire in the middle of the carb. I replaced mine once on a whim and the engine ran better than new. OTOH, I've seen running Tohatsu 3.5's with just a piece of straight stainless wire as a jury rigged replacement.

PS--The symptoms do sound like a possible high voltage breakdown in the ignition system as the spark voltage goes up under load--does the engine just bog down or does it cut in and out??

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Old 07-07-2015, 09:48   #17
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Re: Tohatsu 3.5 no power

I've hed this happen twice for different reasons. First time was due to bad fuel. Second was due to a bad plug. You might also want to check your plug wires / connections.

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Old 07-07-2015, 12:16   #18
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Re: Tohatsu 3.5 no power

Tohatsu power units are used in many other makes of small outboards. I once had a similar problem in another make of outboard. I tried all the usual, carb etc, etc. In my case it turned out to be a faulty ignition suppressor moulded in to the spark plug lead end. The bit that plugs into the top of the spark plug. I simply chopped it off at the lead and from an auto supply I purchased a generic suppressor / connection plug. They screw into the core of the HT lead. It was an instant fix and cost only a couple of dollars. Worth a try. I sealed the join with some clear silicon.

Another thing to check could be water in the fuel tank from rain. Tip out the contents into a container turning the motor completely upside down. If there is water clean out the carb as well.
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Old 07-07-2015, 12:52   #19
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Re: Tohatsu 3.5 no power

Anytime my 4hp Merc has these symptoms I loosen the float bowl drain, and squeeze out a half cup or so using the primer bulb. Runs just fine after that until a little more water accumulates. So I just carry a flat blade screw driver as insurance. I always add Seafoam to the gas, but ...
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Old 07-07-2015, 13:48   #20
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Re: Tohatsu 3.5 no power

I've had similar trouble with my 3.5 hp 2-stroke outboard and small chainsaw (2-stroke). In both cases they ran well after draining the tank and putting in fresh gas.
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Old 08-07-2015, 18:51   #21
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Re: Tohatsu 3.5 no power

I have the same engine and it had the same problem. The above suggestions regarding cleaning the carb are excellent But, If I were you............I'd just buy and install a new carb and you'll be back in business in less than 20 minutes. Why keep fooling with this problem ? It is not all that expensive if you purchase it on line.......
Good luck with it.
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Old 09-07-2015, 05:15   #22
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Re: Tohatsu 3.5 no power

Dear All,

Thank you for your comments. You were all right about the fuel system being the problem. After cleaning the carby, ditching the old fuel and totally cleaning the tank and using new fuel the engine now works as it should. Once again I bow to the collective wisdom of the Forum.

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Old 09-07-2015, 22:14   #23
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Re: Tohatsu 3.5 no power

They are great little engines, lightweight as little engines should be, and reasonably easy and cheap to keep running. In the USA we cant buy new anymore so I'm hoarding my two.

Take two at low eight
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