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Old 08-08-2022, 17:58   #1
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6HP Tohatsu

Any diagnosis suggestions for a 6HP Tohatsu that normally starts up well, runs well for 10 minutes or so and then frequently dies. Once it dies if often will not start. An hour later, or a day later, it often starts right back up and sounds and runs well... until it suddenly dies! TIA

I recently disassembled and cleaned the carburetor and ran even better, but did stall after 15-20 minutes at idle and did have a lot of difficulty starting back up.

The boat also came with two fuel lines and bulbs, and both had the same issue.
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Old 08-08-2022, 18:35   #2
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Re: 6HP Tohatsu

Check your fuel tank to make sure it isn't vacuum locking.
It sounds like the motor starts and runs fine, but fuel supply gets interupted
Only other thing I can think of off hand is the float can sometimes sticks in the full bowl position, not allowing more fuel to flow. That's a little more rare
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Old 08-08-2022, 18:45   #3
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Re: 6HP Tohatsu

Quote:
Originally Posted by chris mac View Post
Check your fuel tank to make sure it isn't vacuum locking.
It sounds like the motor starts and runs fine, but fuel supply gets interupted
Only other thing I can think of off hand is the float can sometimes sticks in the full bowl position, not allowing more fuel to flow. That's a little more rare
If the fuel tank was vacuum locking, would opening the fuel cap fix it (temporarily)? if so, I've tried that, and it didn't help.
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Old 08-08-2022, 18:48   #4
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Re: 6HP Tohatsu

I've got a new carburetor, new fuel pump, new fuel filter, and new fuel tank line with bulb on order. I hope all of those solve the problem...!
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Old 08-08-2022, 19:07   #5
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Re: 6HP Tohatsu

Can also be insufficient or incorrect oil in the fuel mix, causing seizing after the engine heats up.
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Old 08-08-2022, 19:11   #6
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Re: 6HP Tohatsu

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Originally Posted by AndyOz View Post
Can also be insufficient or incorrect oil in the fuel mix, causing seizing after the engine heats up.
It's a 4 stroke 6HP outboard. I'm using 87 octane straight from the automotive gas pump.
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Old 08-08-2022, 19:14   #7
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Re: 6HP Tohatsu

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Originally Posted by quirozson View Post
It's a 4 stroke 6HP outboard. I'm using 87 octane straight from the automotive gas pump.
Ah! That detail would have helped.

So ignore my comment, except you may want to check the lubricating oil quantity and type.
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Old 08-08-2022, 19:14   #8
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Re: 6HP Tohatsu

Did you try running it at max throttle for a while to push the fuel through? At what throttle does it normally die? Did you try using 89 or 91 octane?
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Old 08-08-2022, 19:24   #9
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Re: 6HP Tohatsu

If it runs ok for 10minutes,would it be a fuel problem?
I would be more suspicious of an electronic/electric fault due to a component failing after it gets up to operating temperature.
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Old 08-08-2022, 19:27   #10
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Re: 6HP Tohatsu

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Originally Posted by quirozson View Post
Any diagnosis suggestions for a 6HP Tohatsu that normally starts up well, runs well for 10 minutes or so and then frequently dies.

Hello


I rarely offer troubleshooting advice these days. It is difficult to get it right without being there. So I post with due humility, and also, you're special.


Typically, the symptoms you describe are either caused by fuel starvation due to venting problems (which you have ruled out), or by a broken wire in the magneto. Magneto assemblies that are failing will sometimes/often work OK while cold and then fail when hot. They are made of windings of fine copper wire, and when the wire cracks, it will often work OK until thermal expansion of the magneto assembly causes the crack in the wire to pull apart enough that it no longer conducts electricity, and then there's no spark.


This sort of thing is nearly impossible to diagnose without, just up and replacing the magneto, especially on a one-cylinder engine which is what you have. The problem is that the mag is an expensive part and laborious to swap out due to the fact that you have to pull the flywheel.


That is the reality of the situation, as I see it. Good luck. I am often totally ****ing wrong, even when people pay me for advice, so consider the /src before making any decisions.
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Old 08-08-2022, 19:39   #11
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Re: 6HP Tohatsu

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Originally Posted by Jammer View Post
Hello


I rarely offer troubleshooting advice these days. It is difficult to get it right without being there. So I post with due humility, and also, you're special.


Typically, the symptoms you describe are either caused by fuel starvation due to venting problems (which you have ruled out), or by a broken wire in the magneto. Magneto assemblies that are failing will sometimes/often work OK while cold and then fail when hot. They are made of windings of fine copper wire, and when the wire cracks, it will often work OK until thermal expansion of the magneto assembly causes the crack in the wire to pull apart enough that it no longer conducts electricity, and then there's no spark.


This sort of thing is nearly impossible to diagnose without, just up and replacing the magneto, especially on a one-cylinder engine which is what you have. The problem is that the mag is an expensive part and laborious to swap out due to the fact that you have to pull the flywheel.


That is the reality of the situation, as I see it. Good luck. I am often totally ****ing wrong, even when people pay me for advice, so consider the /src before making any decisions.
Is the part you're concerned about on this diagram?
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Old 08-08-2022, 19:44   #12
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Re: 6HP Tohatsu

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Originally Posted by quirozson View Post
Is the part you're concerned about on this diagram?

Yeah, #30.
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Old 08-08-2022, 19:55   #13
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Re: 6HP Tohatsu

Would one normally just replace the entire assembly in the diagram, or take it apart and replace the possible culprit?

Here is the link to the part you mentioned, which I will consider replacing if my other parts replacements don't address the issue.

https://www.boats.net/product/tohats...e06722d1b726bc
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Old 08-08-2022, 20:04   #14
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Re: 6HP Tohatsu

Per cool hand Luke's question. Is it dieing at idle or 1/4 or 1/2 throttle?
I have the same motor and have found idle to be unreliable with low octane...but the coil/magneto could very likely be the issue.
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Old 08-08-2022, 20:12   #15
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Re: 6HP Tohatsu

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Originally Posted by quirozson View Post
Would one normally just replace the entire assembly in the diagram, or take it apart and replace the possible culprit?

The expensive part is the part that fails, so you buy it however they sell it, Tohatsu apparently sells a kit that includes the (comparatively inexpensive) ignition wire and boot.


I've done the same repair on a couple of older Johnson/Evinrude 2 strokes. They're two cylinder, and the coils are around $50 each, you replace them in pairs. I always bought new cables and boots, and points and condensers (which the newer Tohatsu doesn't use I guess), so it was an expensive repair for an old motor.


Good luclk
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