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Old 13-06-2018, 05:23   #1
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Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Hi folks,

I've been searching around for this, and can't seem to find a similar thread.

The engine will start up just fine, run for 20mins or so, then start to stumble and eventually die. After this it won't restart. Next morning, starts just fine though & cycle repeats.

I'm really hoping it's not the coil as the engine is pretty new, & tbh I'm not able to get a spare at the moment.

I'm running an external tank. Could this be junk in the Carb?

Would much appreciate your opinions



Cheers,

James
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Old 13-06-2018, 05:37   #2
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Extremely unlikely!
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Old 13-06-2018, 05:42   #3
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

A spray can of starter fluid (ethyl ether) is my method for separating fuel supply and carb problems from electrical problems. I'd run the engine until it stops, try to re-start it to prove it will not start, spray some starter fluid into the air intake, and try to start it again. If it will start on ether, it is a fuel supply or carb problem.

By the way, I have the 8 hp 2-cycle Tohatsu and carry a complete spare carb and fuel pump assembly. They are easy to swap and easy to later rebuild.
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Old 13-06-2018, 05:48   #4
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Could it be that the fuel tank vent is clogged or closed?
Try loosening the cap to see if that helps, cause this sounds exactly like a blocked fuel tank vent
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Old 13-06-2018, 05:53   #5
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Thanks. I'll try the fuel tank vent... Its just weird that it won't restart after.. Is that a vapor lock?

I'd try starter fluid, but we're out in the wilds of Tioman in Malaysia at the moment.

Cheers,

James
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Old 13-06-2018, 08:14   #6
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

I had a similar problem with an old Mercury 2 stroke. I'm not sure but I think the crankcase joint started leaking after it warmed up. The crankcase must be sealed so a vacuum can be pulled through the carbs and on the fuel pump diaphragm. Anyhow I ended up replacing the motor.
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Old 13-06-2018, 08:28   #7
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Quote:
Originally Posted by sharpey View Post
Thanks. I'll try the fuel tank vent... Its just weird that it won't restart after.. Is that a vapor lock?

I'd try starter fluid, but we're out in the wilds of Tioman in Malaysia at the moment.

Cheers,

James
You could use fuel instead of starter fluid if not available, just squirt it right down the carb after it quits,if it fires for a second then look at vent or fuel supply. ..sounds like coil if no start after it gets hot...check spark after it shuts down. ..
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Old 13-06-2018, 08:57   #8
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Great advise above, also check for a a bad squeeze bulb on the fuel line or a bad o-ring where the fuel line connects to the engine. I've had both cause problems similiar to yours.
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Old 13-06-2018, 09:07   #9
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

I have a newer 6hp tohatsu 4stroke. Both 2 and 4 stroke are carbureted. Had the same issue with the new EPA limited vent tanks.The vent valve would not release pressure in either direction and ended up with too much fuel being forced into the carb when the tank warms up and no fuel going into the tank when it pressure locks. As a previous poster said just crack the gas cap open( not the vent) before starting and during running. When i'm done I close my cap and I even disconnect the fuel line from the motor other wise it would flood. Ended up just ripping the rubber valve out of the gas cap vent and solved everything. First pull starts everytime and don't think about choking it if it has been running at all.
Things to check
1. do you hear any pressure release when you open thegas cap vent...if yes vent is functioning properly and the above does not apply
2. if no... open your gas cap. do you hear pressure release...if yes then your gas cap vent isn't working.
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Old 13-06-2018, 09:24   #10
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Also check how hot it is getting. Clogged water passages will cause the same symptoms. Usually caused by the impeller shedding a leg.
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Old 13-06-2018, 09:32   #11
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

I had the same problem with my 3hp 2 stroke Tohatsu tried all the actions mentioned above. It turned I had put too much oil when mixing the fuel. Tried a new batch of fuel problem solved, hope this may help, would be interested to hear how you resolve your problem, good luck
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Old 13-06-2018, 09:41   #12
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

I, too, have a 2-stroke Tohatsu 5hp outboard and even though it's not very old, I've had significant troubles with it. When we were in Norfolk, Virginia, we took it to a Tohatsu dealer, who also couldn't fix it. Finally, I took the carburetor off, completely disassembled it, added boiling water to an ultrasonic cleaner, let it clean for a half-hour and then shot all the passages with aerosol carb cleaner. That worked.



I think one problem could be is that the passages and jets on those small carburetors are so small that it takes very little to block them. The Tohatsu dealer in Norfolk blamed fuel that has ethanol added to it.


Good luck, fair winds and calm seas.
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Old 13-06-2018, 09:42   #13
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

Sounds like an ignition issue to me. Like the coil gettting warm. Or ignition module or whatever that engine has.
Also. Just my 2 cents. Donít use starting fluid on a 2 stroke. Doesnít have the oil in it to lubricate things. Your premix has works well.
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Old 13-06-2018, 09:58   #14
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

have you checked your fuel filter
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Old 13-06-2018, 12:42   #15
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Re: Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

I had this problem with my Nissan 6 HP 4 stroke. It was driving me batty until I found the cause.

The external fuel tank had a California Air Resources Board (CARB) approved fuel cap. These newly designed caps have a valve built into the vent that won't allow air to enter the tank until there is a substantial partial vacuum inside the tank. I concluded that the vacuum negative pressure that opens the valve was greater than the pressure created by the fuel pump. So, at the start of operation, the tank would have some residual pressure in the tank, and once that pressure was exhausted by fuel being drawn out of the tank, the engine would sputter as though the fuel was exhausted, and die. This happened every time I used the engine for a while - shorter when the tank was full and longer when it was less than full (more air being present in the tank).

I finally discovered the cause when the engine quit (in accordance with Murphy's Law) at a critical point inside my harbor on a day with a near gale blowing through the harbor. I got an anchor quickly set, and while dangling just feet away from colliding with the Country Sherriff's docked patrol boat, I observed:

1) The primer squeeze pump collapsed when I tried to manually pump fuel.
2) When I tried to take off the fuel cap to visually inspect the tank's fuel quantity, the cap was very difficult to unscrew.
3) A great quantity of air could be heard rushing into the tank, and the tank sides visually expanded, when I finally unscrewed the cap.

Then, after priming, the engine started right up. There was a vacuum in the tank even though the twist vent valve was open. More research and a call to the manufacturer revealed the problem: the cap vent will not let air into or out of the tank until there is a pressure differential. The CARB reasons this will prevent a few molecules of gasoline vapors from entering the environment when the presumed-stupid user doesn't close the vent valve after use. (Murphy's Second Law: "If you make something fool-proof, only a fool will use it.") The only immediate work-around is to leave the cap only partially screwed on - thus allowing a great deal more molecules to continually escape.

Initially, I drilled a hole in the cap and stuffed a plug in the hole when not using the engine. I eventually got ahold of an old-style fuel cap without the pressure-actuated valve.


You can verify you have one of these pressure-actuated valves by removing the fuel cap, opening the twist valve, and trying to gently suck air from the interior side of the cap (sorry about the gasoline taste). If no air passes - you have one of the offending caps.


Another possible cause is a bad seal where the fuel line is attached to the tank. This seal must be airtight if your carburetor is higher than the fuel level in the tank. If the seal isn't tight, the fuel pump will draw fuel only as long as the fuel level is above the carburetor. "Vertical" being a relative thing on any boat that heels, you may first notice this problem when heeled. The cure: fix the seal or place the fuel tank higher than the engine. But your description of the engine starting up the next day indicates this is not the cause.
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