Nissan / Tohatsu 6h 4 stroke - Page 23 - SailNet Community
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post #221 of 257 Old 01-26-2014 Thread Starter
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Re: Nissan / Tohatsu 6h 4 stroke

the alternator is a standard option on the 6hp long shaft I thought... There is no recall that I am aware of..They are good little engines if you don't want or need the full 6hp at the prop. The long or even better ultra long shaft motors are the bomb for sailboats. On this engine I have never had the prop leave the water where on the original johnson 4 hp engine with a 20 inch long shaft it would pop out once in a while in bad seas or really vicious wakes when the boat rolled.

If you had a tohatsu 4 hp then it was the exact same engine as the tohatsu 6 hp.. Actually the 5 hp is also identical.. they are the exact same engine other than different size jets in the carb and maybe a restrictor plate in it.
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Re: Nissan / Tohatsu 6h 4 stroke

Though I liked having the little alternator or maybe better call it a magneto. It only puts out about 1.5 amps current at most rpms that you would use for any length of time. It only puts out the 4 to 5 amps when at full rpm which wont happen with this engine unless it is in neutral. If you look in the manual you will see that it specifies that it isn't really used for charging batteries or anything. It's just there to run instruments and running lights on a runabout/dingy etc.. I hooked it and a 20 watt solar panel up to a charge controller and between the two on a long trip might get about 2.5 to 3 amps at best charging current back into the batteries (at best).
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post #223 of 257 Old 01-26-2014
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Re: Nissan / Tohatsu 6h 4 stroke

If anyone did the homework they know that the alternator is not going to charge a battery bank to run a microwave and ac on the yacht. I did not buy my 6hp with one. It could be nice for some one that wants to motor in at night. It will run lights. They seem to offer this engine in as many custom ways you could ask for 4,5,6 HP long, short shafts. with or without a gas tank. The price is reasonable less cost than some 4hp engines If you do not like it you can buy any other engine you wish.
So far I like this engine. It runs, it starts, it moves the boat that is all I ask.
What am I missing. Should I be unhappy ?
Kind Regards, Lou
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post #224 of 257 Old 01-27-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Gentlemen- I have read through a lot of this thread. I have little experience with outboards but a LOT with motorcycles. And Honda, Yamaha, Suzuki are motorcycle manufacturers first and foremost. And Tohatsu did some too back some years. But in order to compete with the big guys they must at least equal their knowledge and technology.
My point is: the Tohatsu 6hp is 123cc and oversquare. Which means the cylinder bore is larger that the stroke. This is a common- almost the rule- for japanese engines. And it is conducive to high rpms.
The bottom line: japanese motorcycles of this configuration were turning over 15,000 rpms and running over 100mph 40 YEARS AGO!!!! Yes single cylinder ones too! To find one which can't turn 6,000rpm is.....amazing! And he dropped the pitch from an 8 down to a 6 and got no appreciable improvement? Something is wrong here! And I notice a post some pages ago in which a man stated he was making a distance run and his motor suddenly picked up power and speed but never did it again before or since. I suggest there is something in the intake tract or the carburator which is the culprit. Is the Tohatsu like the old OMC products and has no air cleaner? That is a common factor on motorcycles but if there is none then it is eliminated as a factor. I would like to see what the spark plug looks like. Being water cooled this engine may be running very lean. Lean running being conducive to heat. And reduced emissions which is why it is so common- nay the rule nowadays. The excellent fuel economy you all mention is an indicator too. I second the motion that you put in a larger jet. If the carburator is like the ones in a motorcycle there are 2 jets. The idle or slow speed jet and the main jet which controls half to full throttle operation. Change the main jet- leave the other alone. There is my 2 cents lol.
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post #225 of 257 Old 01-27-2014
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Re: Nissan / Tohatsu 6h 4 stroke

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Originally Posted by audeojude View Post
the alternator is a standard option on the 6hp long shaft I thought... There is no recall that I am aware of..They are good little engines if you don't want or need the full 6hp at the prop. The long or even better ultra long shaft motors are the bomb for sailboats. On this engine I have never had the prop leave the water where on the original johnson 4 hp engine with a 20 inch long shaft it would pop out once in a while in bad seas or really vicious wakes when the boat rolled.

If you had a tohatsu 4 hp then it was the exact same engine as the tohatsu 6 hp.. Actually the 5 hp is also identical.. they are the exact same engine other than different size jets in the carb and maybe a restrictor plate in it.
No. The alternator is only standard on the UL SailPro.

Yes, the MFS4,5,6 are the same block.

No. They are 3 different carbs; one each for the 4, 5, and 6. The throats are different sizes. If you change to the wrong jets, all you will accomplish is the wrong mixtures. Period.
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post #226 of 257 Old 01-27-2014
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Re: Nissan / Tohatsu 6h 4 stroke

yeoup, you can get a little more oomph by simply chainging the main jet on this outboard and most alike...

but if one doesnt want to well thats their call huh

in any case, many ways to get a little more oomph

changing to a bigger throat(intake) and changing the main jet acoordingly for WOT or close to it will give you what johnson did back in the 80s and 90s

2 engines in one block

a 9.9 and a 15hp, absolute only difference was this above, throat size, main jet and a few other small things to get about 1000rpm or so more at wot

again correctly prop it for sure...

solas props do a nice job of offering a variety of props for every situation

peace

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post #227 of 257 Old 01-27-2014 Thread Starter
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Re: Nissan / Tohatsu 6h 4 stroke

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Originally Posted by Lou452 View Post
So far I like this engine. It runs, it starts, it moves the boat that is all I ask.
What am I missing. Should I be unhappy ?
Kind Regards, Lou
no you shouldn't be unhappy.. Like I have said before if the engine performs adequately for you and you don't need the full rated power then it's a great little engine. Runs all day long, sips fuel, starts easy....
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Re: Nissan / Tohatsu 6h 4 stroke

99% of everyone wouldn't even notice that it is underpowered. The only reason I did is that I bought it specifically to bump my power up a bit from the 4hp I had. It going from 6.1 knots or so down to 5.2 knots when I put this engine on the boat was a bit of a shock. After playing with it for 6 months and multiple props dropping the pitch each time I finally got it up to just a hair under equivalent performance of my old 4hp.

Interesting suggestions on the jets.. I have thought about it before but didn't really know enough about doing it myself to be more than dangerous. I don't doubt that the engine is capable of 6hp. Just wish it came from the factory that way, since that is what I paid for.. Significant premium on the 6hp over the same engine in 4 or 5 hp.
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post #229 of 257 Old 01-27-2014
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Re: Nissan / Tohatsu 6h 4 stroke

I have the 8hp Tohasu on my Hunter 23.5 and it won't rev out either. However it will push my boat at 6 knots in smooth water at half throttle. Trying to open the throttle more doesn't do much. The engine is smooth and quiet being a 2 cyl. But even this larger engine is not producing all it's horsepower on my boat. The old Johnson 4 hp two stroke I had before would push it almost as well but used a lot more fuel and was working harder. The little Johnson works very well on my 16' Sunbird.

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post #230 of 257 Old 01-27-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Rejetting the carbs isn't rocket science. It is routinely done on motorcycles. Every bike you see with aftermarket exhaust (that means probly 75% of em) has been rejetted- or should have been. There are kits for the purpose.
I work on bikes which have 4 carburetors. Tear em all apart and put em back together. And these boat engines don't have the constant velocity system. At least not the ones I've seen.
I'm sure Tohatsu doesn't have a carb specifically designed for this motor. They select from what is produced by Mikuni or Keihin or whoever. I bet its an even chance that the motors which run well have a different carb than the poor running ones.
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