SailNet Community

SailNet Community (
-   Gear & Maintenance (
-   -   Tohastsu - 8hp 4cycle - tech questions (

LarryandSusanMacDonald 11-23-2009 01:04 PM

Tohastsu - 8hp 4cycle - tech questions
Here's the story - purchased the Tohatsu 8hp 4 cycle last summer - so it's relatively new.

Used it frequently traveling on the Chesapeake and down the ICW. All of a sudden, it would not run slow. It would start right up, first pull, but when taking it down to idle to put it into gear, it stalls.

A friend who has the same engine told me that he had the same problem and it cost about $200.00 for a mechanic to fix it. Apparently, the slow jet in the carburetor clogs because of ethanol in the fuel.

I got busy and downloaded the parts manual PDF, located the slow jet, removed it - cleaned it, put it back together, and miracle of miracles, it worked!


Damn. I mean, darn.

I thought maybe the idle had to be adjusted - but not so. And I hate to take the carburetor apart every time it clogs - which so far is every time.

My questions:

Is there something I'm missing / don't understand?

Is there a downloadable repair manual on line anywhere? I can't find one.

Is there some kind of fuel additive, or cleaner that I could add to the fuel or spray in the air cleaner? (I have been told there is not - but not by professionals.)

Apparently I need to purchase non-ethanol fuel in the future to prevent this from happening. I am told that marinas in the south have it. Is this true? And what do I do when I get back north where apparently it is not available?

Is there some kind of slow jet for that engine which would accommodate the ethanol fuel?

Am I asking too many questions?

Right now, we're sitting at anchor in St. Augustine and the weather is beautiful - and we can't go to shore cause the dinghy engine is crapped. Soon, I will probably feel the wrath of Saltwater Suzi, so, HELP!!!

tommays 11-23-2009 01:14 PM

The service manuals are copyright :)

But anyway there is usally a rubber plug on the motor housing that lets a screwdriver reach the drain screw for the carb bowl.

It does NOT have to be removed only opened a few turns as it has a drain hole drilled in it for this

I use some paper towles so the fule does not get into the water .

Pretty much any new motor has this issue as to meet the new 3 star EPA rules there really LEAN :(

tager 11-23-2009 01:20 PM

I would put some seafoam in the fuel, and make sure to run the carb dry every once in a while. It may save you the trouble of draining the float bowl. Just turn the petcock or unplug the fuel line and run it in neutral until it dies. This should keep the carb reasonably clean.

LarryandSusanMacDonald 11-23-2009 01:21 PM


I expected that I couldn't get a manual for free - but they only want to mail it to me - which, since we use a mail forwarder, could take weeks.

How does draining the fuel in the carburetor help the problem - I don't understand. (Is it becoming obvious that I'm really no mechanic - just a cheap, struggling DIYer.)

Just found a link about Starbrite's Star Tron. I actually have some and used it to forestall this problem - do I need to use more?

eherlihy 11-23-2009 01:23 PM

What ethanol does is a bunch of things;
First, it is a solvent that will eat many rubber compounds. It turns pliable rubber in your carb gasket, or fuel line, or needle valve into a sticky goo. This goo can travel through your fuel system and clog the jet. To solve this, you can replace any rubber parts that are prone to alcohol degredation with different rubber compounds which are not. It'll probably cost less than $50 in parts.

Second, because it's a solvent, it can loosen other gunk that has been hiding in the fuel system. This gunk, now set free, travels through the fuel system and gets stuck in the narrowest of spaces, kind of like a blood clot causes a heart attack. The narrowest spot in the fuel system is the idle jet. Adding an in-line fuel filter can help address this problem.

Third, while oil and water don't mix, alcohol and water do. Because of the high humidity ever present in boating this can be a real problem. This water can cause corrosion anywhere in the fuel system. The solution to this is at the end of the day to not shut the motor down with the kill switch, but cut the fuel (shutoff) and run the engine until it stalls.


- Ed

LarryandSusanMacDonald 11-23-2009 01:23 PM


That's two in favor of draining the carb bowl. I'll give it a try. What's seafoam?

LarryandSusanMacDonald 11-23-2009 01:32 PM


I would have expected that on a new engine, they would already have installed the higher quality rubber parts. You're probably right though - I'll see if I can find out from Tohatsu.

I have installed a fuel filter in line - but no a water separator. I didn't think it would do much good since the water is mixed with the ethanol which is suspended in the fuel. That may be something else I'll have to work on.

There shouldn't have been too much gunk in the tank because it came new with the engine.

Your third suggestion - running the carb dry I'll try and maybe that will help. Once I get past the current problem.

Thank you all so far. Really appreciate your input.

tommays 11-23-2009 01:43 PM

Its a new motor and NONE of the parts should have any E10 issues as they were built for it

Running the motor till it stalls leaves the bowl about 1/2 full and more prone to the issue.

There is small inline filter in the motor and if your keep having issues the next step is to go with a full size water separtor which would be a bit of a PITA on and 8 HP motor

Seafoam is like Sta-bil in thats its been around forever but nobody can really tell you how it performs what it claims as seafoam has a well know MSDS that tells you whats in it Pale oil and Naphtha :) and Sta-bil is just RED Naphtha

tager 11-23-2009 01:44 PM

Here is some more information about seafoam and it's use in ethanol mixed fuel. Basically it is fuel stabilizer that stops "goop" from clogging your jets as well as myriad other things. Draining the carb bowl is achieved by doing exactly what eherlihy said. It runs the carb dry so that there is no solvent sitting in there eating away at your rubber parts.

A carburetor is intended to control the fuel-air mixture entering the cylinder. Apparently the ethanol in your fuel is causing a problem with one of your jets. One option is to clean the carb all the time. The easier options, (which forestall cleaning) are to add seafoam, and drain the carb every time it is used.

When fuel is left in the float bowl of your carb, it sits there, dissolving your rubber parts, and creating a gooey varnish that is the premature death of many outboards. This causes the carb to stop functioning properly, so your cylinder is not receiving the right fuel/air mixture at low idle, hence it "starves" to death.

eherlihy 11-23-2009 02:17 PM


Originally Posted by tommays (Post 544689)
Its a new motor and NONE of the parts should have any E10 issues as they were built for it

:rolleyes: Uh, no...
At least not as of 2007, the latest year service manual that I could find;

Fuel and Gasolin

Premium (super) gasoline is highly recommended for TOHATSU motors. Fuel should be a minimum pump posted Octane Rating of 87 (91 by Research Octane Rating).
Gasoline containing alcohole [sic], methanol (methyl), or ethanol (ethyl) may cause;
* Wear and damage on bearings, piston, piston rings, and cylinder liners.
* Corrosion on metal parts
*Deterioration on rubber parts and plastic parts

Note: Engine damage resulting from the use of fuel containing such alcohl(s) is not the responsibility of TOHATSU, and will not be covered under the limited warranty.

I had to re-type this, because I don't have Acrobat on this PC. I tried to capture all their mis-spellings (and there are quite a few!)

Tohatsu is not the only outboard maker with a propensity to damage from alcohol with their recent motors.

- Ed

All times are GMT -4. The time now is 06:13 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
(c) LLC 2000-2012

For the best viewing experience please update your browser to Google Chrome