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Old 06-07-2015, 07:56   #1
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Tohatsu 3.5 no power

Dear All - would love your feedback on my Tohatsu 3.5B2 outboard. I can't get any power when I click into gear. I've cleaned the carbie and she revs well in neutral. Starts easily and idles well, but when I put her in gear and try to open the throttle she sounds like she wants to stall. She'll trudge along at low revs, but this doesn't seem right. I've changed the gearbox oil but have run out of ideas. Any suggestions on what's wrong?
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Old 06-07-2015, 08:12   #2
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Re: Tohatsu 3.5 no power

Sounds like a clogged jet in the carb which may have escaped the cleaning process. Otherwise possibly clogged fuel filter (located where hose connects to tank).

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Old 06-07-2015, 08:30   #3
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Re: Tohatsu 3.5 no power

Or the mixture has gotten out of whack.....easy adjustment too.


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Old 06-07-2015, 10:28   #4
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Re: Tohatsu 3.5 no power

I have two of them, one is 12 years old and the other 16. Any problem I have ever had has been fuel system related. Start there.
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Old 06-07-2015, 11:30   #5
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Re: Tohatsu 3.5 no power

Thanks guys,
I've recleaned the carbie and checked the fuel lines. All seems good, and in neutral she'll rev up very easily and hold the revs well. But.... as soon as I drop the revs and put the engine in gear she threatens to stall. Once in neutral again the engine revs freely. So not sure if it's the fuel system. Any other thoughts? Cheers
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Old 06-07-2015, 11:34   #6
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Re: Tohatsu 3.5 no power

I have a merc 9.8 with the same problem. I've cleaned everything and noticed the points are a little cooked in mine. I still have not picked up or found new points but that is where I'm going to attempt next.
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Old 06-07-2015, 12:02   #7
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Re: Tohatsu 3.5 no power

I think you are failing to clean out whatever is blocking the main jet. The idle circuit is a different one. It will idle and rev up in neutral, on the idle jet. But when you put it in gear, the main jet(s) kicks in.

The trouble is that these modern small 4 strokes have very small jets that are extremely difficult to clean.

I had a brand new Suzuki 2.5 with the same problem. The dealer changed the carb and it was fine.

Either buy a new jet, or a new carb.

Have you been following good practice with the fuel? Add a stabiliser, keep the gas fresh (I put it in the car when it's more than a month or two old) and always run the carb dry. This will reduce future problems.
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Old 06-07-2015, 12:18   #8
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Re: Tohatsu 3.5 no power

Thanks MarkSF. I forgot to mention that the engine is a 2 stroke. But I take your point about the fuel cleanliness. I always turn the fuel off and let the engine run dry.
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Old 06-07-2015, 12:30   #9
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Re: Tohatsu 3.5 no power

I am not an engine guy by any means, but have you checked if the prop can rotate properly. If you wrapped any line in it, then in gear you would have that problem but not in neutral.
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Old 06-07-2015, 12:37   #10
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Re: Tohatsu 3.5 no power

I would still suggest changing the main jet. If that doesn't fix it, I have heard of this problem being caused by a weak spark from the magneto. The spark is enough at idle, but when more fuel/air mixture is added, it cannot jump the plug gap.

Saw this ignition problem just last week on my friend's Miata. Idled perfectly, stalled as soon as you tried to drive it.

So in order I would suggest :

Change the main jet
If that doesn't fit it, change the magneto.
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Old 06-07-2015, 15:55   #11
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Re: Tohatsu 3.5 no power

I too would bet on the carb; the high speed circuit in particular. Pull the carb off (again) remove the bowl and float, put the carb (but not the float or needle valve) in a pot of water with a squirt of Joy dish washing detergent, boil it on the stove for 30 minutes, then put everything back together. If you have access to compressed air, blow thru every hole you see before you reassemble the carb. If not, don't worry to much.

I own one of these.
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Old 06-07-2015, 16:13   #12
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Re: Tohatsu 3.5 no power

You can check if something is amiss in the lower end by removing the spark plug and pulling the starter cord both in neutral and in gear.
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Old 07-07-2015, 05:39   #13
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Re: Tohatsu 3.5 no power

Outboard dies when throttling up from idle
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Old 07-07-2015, 09:26   #14
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Re: Tohatsu 3.5 no power

I just spent 2 days working on a neighbors 7 hp Tohatsu. Similar problem. Problem arose when switching out fuel tanks. After new plugs, carburetor cleaning, etc. decided to dump the fuel and noticed on the Tohatsu fuel tank the mixture was 100/1. Mixed new fuel at the correct mixture as the owner said he hadn't paid any attention to the mixture and " just threw in a can of 50/1 2 cycle oil ". Ran like a new motor as soon the old gas was cleaned out.

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Old 07-07-2015, 09:27   #15
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Re: Tohatsu 3.5 no power

If the engine revs in neutral it is not likely the high speed jet. Check the off idle ports with a small piece tag wire if you don't have access to compressed air as a small speck of dirt will cause the engine to stall or bog when you try to throttle up
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