6HP Tohatsu

[sailhand]

The main problem I see is fuel. Ethanol is a big contributor also not keeping fuel well sealed which prevents condensation in the drum/tank of a night time which runs down under the fuel and cannott evaporate from under there so its like a mini watermaker. I also try not to agitate fuel in drums before dispensing into tanks and never use the last litre or so. I decant that into another jerry can reserved for that purpose and within months l end up with half a litre of water and gunk in the bottom of that drum. I still decant/use the fuel from this drum after its nearly full of all the dregs however I am very careful not to agitate it before decanting keeping the sludge and water in the bottom of the drum. The last litre of this drum goes into an empty clear plastic milk bottle. Inevitably there is always nearly half a litre of gunk in the milk bottle. I also have two inline filters at least between fuel tank and motor, especially on the smaller built in tanks under the cowling. All this tends to keep my carby rebuilds to a minimum. Of course the other big fuel system killer is long periods with no use and dried varnished fuel in the system. This can be in fuel lines and filters, tanks and carbies. A carby cleaned and hooked onto the existing previous same fuel source is usually a waste of time and fills the nice clean carb full of gunk almost immediately. Also a great little diagnostic tool is a can of engine starter. If your motor stops squirt some in the air intake and try and start it. If it fires then you have a fuel problem, if not its spark. You need three things, air fuel and spark if you can guarantee that you have two at least then its easier to isolate the problem. Make sure you dont have the choke on when you try the engine starter fluid as it prevents air and starter fluid mixture entering the cylinder. Cheers

[betwys1]

Originally Posted by quirozson

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.

Replace float in carb.

[Nickodemus]

We had the exact same problem on our 20 hp Tohatsu and it was the THERMOSTAT!! Good luck getting one. Severely back ordered.

[The Sun King]

Ignition coil?

[DSCYP]

Originally Posted by sailhand

The main problem I see is fuel. Ethanol is a big contributor also not keeping fuel well sealed which prevents condensation in the drum/tank of a night time which runs down under the fuel and cannott evaporate from under there so its like a mini watermaker. I also try not to agitate fuel in drums before dispensing into tanks and never use the last litre or so. I decant that into another jerry can reserved for that purpose and within months l end up with half a litre of water and gunk in the bottom of that drum. I still decant/use the fuel from this drum after its nearly full of all the dregs however I am very careful not to agitate it before decanting keeping the sludge and water in the bottom of the drum. The last litre of this drum goes into an empty clear plastic milk bottle. Inevitably there is always nearly half a litre of gunk in the milk bottle. I also have two inline filters at least between fuel tank and motor, especially on the smaller built in tanks under the cowling. All this tends to keep my carby rebuilds to a minimum. Of course the other big fuel system killer is long periods with no use and dried varnished fuel in the system. This can be in fuel lines and filters, tanks and carbies. A carby cleaned and hooked onto the existing previous same fuel source is usually a waste of time and fills the nice clean carb full of gunk almost immediately. Also a great little diagnostic tool is a can of engine starter. If your motor stops squirt some in the air intake and try and start it. If it fires then you have a fuel problem, if not its spark. You need three things, air fuel and spark if you can guarantee that you have two at least then its easier to isolate the problem. Make sure you dont have the choke on when you try the engine starter fluid as it prevents air and starter fluid mixture entering the cylinder. Cheers

In addition to all the above [great] information, I've found that changing the spark plug each season appears to prevent this problem. Always use non-Ethanol fuel. Always add the recommended amount of Seafoam to each tank.

[Ratty1978]

Don't know all your plumbing arrangements, but I'd look for a filter somewhere.

[BoatBumm]

I mostly agree with Jammer about an internally broken magneto wire that loses conductivity as the engine warms up, but I disagree that that’s hard to diagnose.

Pull the spark plug wire loose when the engine is cold and experiment with what you have to do to see a spark jump to the engine when someone cranks the motor (pulls the starter cord). Sometimes the only way to see it is to do this test after dark. Running the engine on a stand rather than the boat while you do this might also make life easier.

Then replace the spark plug wire, start the engine, let it run until it dies, then immediately, before everything cools off, check again for a spark. .

If there is still a good spark - cross that off the list. If no spark you’ve made the diagnosis.

I’d also, just to be sure, try a different fuel tank. Unlikely that’s the problem, but should be easy to do. Something might be somehow blocking the fuel pickup.

[White Rabbit]

I have a 6 hp Tohatsu which had the same symptoms. The problem was inside the fuel line. Must have been the alcohol in the gas. The fuel line looked perfectly normal on the outside but when I sliced it open, I found that the fuel line on the inside had peeled away and form a blockage. Looked like a tricuspid heart valve. I replaced all the molded fuel lines. I tried to use regular fuel line to save money but unfortunately, the line couldn't make the bends so I had to buy the Tohatsu molded fuel lines.

The other problem I had is that the fuel pump failed. I could get the engine started but then it would die after a few minutes. This happened after I replaced the fuel line. Might be that the fuel pump was damaged by working so hard pushing and sucking fuel through the bad fuel line. Now my engine runs great.

A maintenance/operations item is run the engine until the fuel is used up in the carburetor bowl when you are not using the engine for any length of time. The carburetor passages are so small that they get plugged up if the fuel dries up inside the carburetor. I used to have to take apart and clean the engine at the beginning of every season and also if I left the engine sitting for one or two months. Now I don't have a problem.

[Lake Effect]

Check for spark after the motor dies. If you have spark then that’s not the problem.
If you can get the motor to run by pumping the primming bulb continuously, then your fuel pump is bad.
I have a brand new 8hp Tohatsu that had a bad fuel pump replaced on warranty. The dealer cleaned the carb to no avail. He didn’t want to put on a new fuel pump because “they never go bad”. A new pump fixed it right up. It’s a great motor now.

[Eben]

Originally Posted by quirozson

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.

I had the same issue, this happened after I put the motor down on the wrong side. It was oil in the carb, not much but just enough to cause issue. I took it apart and cleaned it out with petrol, no issues since.

[tjamaco]

I had a similar issue and discovered, after much anger, profanity, consultation, expense and bewilderment, that the tank fuel pickup was not firmly lodged in the transfer orifice. Silicone sealant solved the issue.

[Pleasure II]

Sounds like you may have water in the fuel tank. Suggest you empty it, clean out the carby and try again.
Good luck.

[Seaward22]

Have the same motor (Nissan 6A2S). Motor has always had idle issues, have to run near the midway throttle mark when warm and quick decrease flip when shifting. When warm throttle has to be at midway mark to start. Run 87 with stabilizer.

[Antipodean2]

Hi

I only use a high octane around 91 or 95, and don’t use ethanol or bio fuel.

Keep your fuel fresh, if 2 stroke mix at correct ratios.

Good luck!

[rslifkin]

Originally Posted by Seaward22

Have the same motor (Nissan 6A2S). Motor has always had idle issues, have to run near the midway throttle mark when warm and quick decrease flip when shifting. When warm throttle has to be at midway mark to start. Run 87 with stabilizer.

There's definitely something up with yours, probably a carb issue. I've got the later C model (which runs even leaner) and it idles like a Swiss watch. Cold starts are a little fussy, as it's always a guess about whether it will want full choke, partial choke, or no choke but a little throttle. When it's even a little bit still warm from a previous run, set the throttle to the restart mark (probably 1/8 throttle), give it a pull and it fires right up. As soon as the revs start to build a bit, throttle back to idle and it's good to go.