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  #241  
Old 01-28-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Quote:
Originally Posted by christian.hess View Post
do you want me to show you the page where johnson SPECIFICALLY says this is so Im not arguing...I agree....the bes way is to change carb completely however on some engines, specifically the one I mentioned

the johnosn 9.9 and 15 series its simply carb jet size and manifold...NOT CARB

Like others have posted before and have experience in this(I restore motocrcyles too) you can absolutely depending on where adjust your jet sizes for performance where you need it(most carbs come jetted for sea level naturally) if you are in a lake up in tahoe it makes sense to do your due dilligence and rejet...

the correct jets however are almost NEVER installed in your carb, especially if you live in countries like the good ole use or europe where epa and other nuissances DICATATE what power and emmissions you can get from a certain engine especially when its sold commercially to major areas.

so i disagree...but thats ok...to disagree....

this also comes from experience in small engine rebuilding...on water and off

for example most carbs especially on motorcycles these days have specific kits called smog block off kits, evap removal kits or in some cases even pilot jet cap removal kits as some carbs are soooooooo EPA compliant that they wont even let the owner fine tune the slow jet for easy starting depending on your altitude and climate

lets not even go there...its very easy to get a little more oopmh from these simple engines...especially once you have propped right

here is another tidbit

saying the jets that come with all outboards are perfect makes no sense...especally since many dinghy outboards for example used at idle when they were designed to run at wot or 3/4 foul plugs up naturally, especially if 2 stroke and hence why most older outboards had nice rich lean knobs to fine tune your idle mixture

if yo were a diligent owner you did this every time you started and stopped the engine

just sayin

not here to argue just offer my point of view...and experience

cheers
Not even close to being an expert on anything, but do have 30 years of experience with off road motorcycles, nine of them, two of which were 4 strokes. About 66 years experience with outboards, ten of them, two of which were 4 strokes. Changed a lot of jets, primarily because of altitude changes.
Last 2 stroke I had with an adjustable high speed jet was a 1959 50 HP 2 stroke Evinrude. Anyway, what I found, in general, was that the factory installed jetting or setting, was spot on at sea level.

My last 4 stroke motorcycle, a Honda 200, ran perfectly at sea level but loaded up at 6,000 feet. A lower restrictive exhaust system was the only thing that solved the problem, re-jetting helped a bit more.

I think that if there is something wrong with the OP's motor, the stock jetting would the last thing I would try changing. The 6HP 4 stroke Tohatsu I bought a year or so ago ran perfectly right out of the box, both at sea level and at 6,000 feet elevation. Don't know how many props the OP has tried but Pvan1's suggestions on props is where I would start.

Paul T
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  #242  
Old 01-28-2014
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Re: Nissan / Tohatsu 6h 4 stroke

threads like this are just like threads on mc forums...not worth it

suffice it to say that not all engines are created equal...not all bikes or boats are created equal and not even the same jets in the same engine side by side are created equal

engines and carbs for for outboards and most bikes, are bench tested and sent from the factory according to emissions standards nowadays

if you think your engine is jetted perfectly from the factory for ease of starting...slow idle...wot etc...well you are wrong

again I STRESS that outboards and most engines are jetted for overall performance

certainly not for max performance anywhere

but thats the great thing...you jet for overall err SAFE

Im laughing at myself as I type this cause I would always err on the safe side on mc forums quoting that standard jetting was always better for overall performance give or take a few tweaks of the fuel mix screw or pilot jet or main depending on what and where your rode

in any case outboards do perform well with stock jetting for 99 percent of people

its that 1 percent that nags and wants more

I guess thats all I was trying to say

I understand that being an outboard tech now has more weight than what anyone else here says myself included...but based on past experience Im glad to say that reality is differnt from techincal fact...or THEORY if you will

life is that way also

just cause you have a 6hp outboard means squat when you can make a 4hp perform equally and more efficiently...

just sayin

dont shoot the messenger

notice the first thing I recomended was a nice 4 blade solas prop?

this would put the op on the rpm range he wants, if still not enough then he could tweak the jetting for example

but who cares now
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  #243  
Old 01-29-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Quote:
Originally Posted by christian.hess View Post
do you want me to show you the page where johnson SPECIFICALLY says this is so Im not arguing...I agree....the bes way is to change carb completely however on some engines, specifically the one I mentioned

the johnosn 9.9 and 15 series its simply carb jet size and manifold...NOT CARB

Like others have posted before and have experience in this(I restore motocrcyles too) you can absolutely depending on where adjust your jet sizes for performance where you need it(most carbs come jetted for sea level naturally) if you are in a lake up in tahoe it makes sense to do your due dilligence and rejet...

the correct jets however are almost NEVER installed in your carb, especially if you live in countries like the good ole use or europe where epa and other nuissances DICATATE what power and emmissions you can get from a certain engine especially when its sold commercially to major areas.

so i disagree...but thats ok...to disagree....

this also comes from experience in small engine rebuilding...on water and off

for example most carbs especially on motorcycles these days have specific kits called smog block off kits, evap removal kits or in some cases even pilot jet cap removal kits as some carbs are soooooooo EPA compliant that they wont even let the owner fine tune the slow jet for easy starting depending on your altitude and climate

lets not even go there...its very easy to get a little more oopmh from these simple engines...especially once you have propped right

here is another tidbit

saying the jets that come with all outboards are perfect makes no sense...especally since many dinghy outboards for example used at idle when they were designed to run at wot or 3/4 foul plugs up naturally, especially if 2 stroke and hence why most older outboards had nice rich lean knobs to fine tune your idle mixture

if yo were a diligent owner you did this every time you started and stopped the engine

just sayin

not here to argue just offer my point of view...and experience

cheers
A 2-cylinder 2-smoke OMC 9.9/15 is a completely different animal from a 1-cylinder 4-stroke Tohatsu. On the Tohatsu, one swaps carbs for different CFM delivery... on some OMC models, the CFM is determined by the intake. Yes, air-cooled cycles can sometimes benefit from final re-jetting based on gear ratio, elevation, temperatures, etc. If the MFS 4/5/6 is used near sea level (and they do run a bit cold in the crankcase, but OK in the chamber), swapping to a richer jet will definitely foul the plug. Outboards are always loaded, never coast, and are in a rough environment -- and they can't downshift. I service hundreds of these a year, so I obviously have no experience with the Tohatsu 4-strokes.
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  #244  
Old 01-29-2014
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Re: Nissan / Tohatsu 6h 4 stroke

did I ever say you werent...?

just offering a different opinion dude...you are a technician for tohatsu great good for you...

I just dont understand when one is asking questions why there is always the need to only have one answer...

there is no one answer especially when the OP has issues with his engine or not, real or not...4 stroke or not...its still an outboard that is not performing to his standards...

a lot of people for example complain that 4 strokes have a lack of power when compared to 2 strokes...what is common here is that 2 stroke are revvers 4 strokers are torquers...

so it might simply be that the op is not used to smooth 4 strokes that never really reev out...especially the little ones...

all I was saying from the beginning is that he should prop right, slam a good tach on it...

do some testing with different props and setups and maybe just maybe take a look at whats going on with the intake and carb...

ih he doesnt want to do that cool

no sense arguing or offerig advice or whatever...and no sense arguing with you as I didnt even intend to!

peace
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  #245  
Old 01-29-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Quote:
Originally Posted by pvanv1 View Post
A 2-cylinder 2-smoke OMC 9.9/15 is a completely different animal from a 1-cylinder 4-stroke Tohatsu. On the Tohatsu, one swaps carbs for different CFM delivery... on some OMC models, the CFM is determined by the intake. Yes, air-cooled cycles can sometimes benefit from final re-jetting based on gear ratio, elevation, temperatures, etc. If the MFS 4/5/6 is used near sea level (and they do run a bit cold in the crankcase, but OK in the chamber), swapping to a richer jet will definitely foul the plug. Outboards are always loaded, never coast, and are in a rough environment -- and they can't downshift. I service hundreds of these a year, so I obviously have no experience with the Tohatsu 4-strokes.
just sayin tech or not this is a false statement

anywhoo carry on
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  #246  
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Re: Nissan / Tohatsu 6h 4 stroke

So, if the OP is still reading this, perhaps he could tell us what, if anything, he has tried recently, prop sizes, pitch, etc?

Paul T
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  #247  
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Re: Nissan / Tohatsu 6h 4 stroke

Quote:
Originally Posted by christian.hess View Post
threads like this are just like threads on mc forums...not worth it

suffice it to say that not all engines are created equal...not all bikes or boats are created equal and not even the same jets in the same engine side by side are created equal

engines and carbs for for outboards and most bikes, are bench tested and sent from the factory according to emissions standards nowadays

if you think your engine is jetted perfectly from the factory for ease of starting...slow idle...wot etc...well you are wrong

again I STRESS that outboards and most engines are jetted for overall performance

certainly not for max performance anywhere

but thats the great thing...you jet for overall err SAFE

Im laughing at myself as I type this cause I would always err on the safe side on mc forums quoting that standard jetting was always better for overall performance give or take a few tweaks of the fuel mix screw or pilot jet or main depending on what and where your rode

in any case outboards do perform well with stock jetting for 99 percent of people

its that 1 percent that nags and wants more

I guess thats all I was trying to say

I understand that being an outboard tech now has more weight than what anyone else here says myself included...but based on past experience Im glad to say that reality is differnt from techincal fact...or THEORY if you will

life is that way also

just cause you have a 6hp outboard means squat when you can make a 4hp perform equally and more efficiently...

just sayin

dont shoot the messenger

notice the first thing I recomended was a nice 4 blade solas prop?

this would put the op on the rpm range he wants, if still not enough then he could tweak the jetting for example

but who cares now
Only speaking from my own experiences, to share with the OP. If he can gain anything from them, that is good. Agree on the motorcycle thing, changed a few carbs, Amal & Bing to Mikunis and jetting to suit altitude and various courses.

As Pvan1 mentioned, generally speaking, outboards are run pretty hard, maybe with the exception for trolling all day, followed by an hour WOT run home. Jetting is easy to do, but if you get it too lean, it can be costly.

My opinion, offered at no cost, and for what it is worth.

Paul T
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  #248  
Old 01-30-2014
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Re: Nissan / Tohatsu 6h 4 stroke

Why did have to look at this thread? Years since I've looked at it and it's still the same BS
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  #249  
Old 01-30-2014
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Re: Nissan / Tohatsu 6h 4 stroke

A bit OT, but, since it seems that this thread is still being read, and my request to start an outboard sticky is being reviewed by the mods, I'll ask it here. I have a 1976 Evinrude 6hp Short Shaft. I have the opportunity to purchase a 1974 Johnson 6hp Long Shaft advertised for sale for "parts" (it turns but will not start). Seller wants $100. Based on what is available research wise, it would seem that I could make my short shaft in to a long shaft if I cannibalize it. Or, I could diagnose whatever the problem is, repair it, and then have two outboards. Which would be optimal for my dinghy. Advice? Yes? No? Is there a flaw in my carefully planned takeover of the 6hp used outboard market in SoCal?
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  #250  
Old 01-30-2014
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Re: Nissan / Tohatsu 6h 4 stroke

I have a '71 long shaft Johnson 6hp and have been doing research. There is enough info on the 'net that one could rebuild these motors top to bottom. I can't answer your question because it depends on the condition of this 2nd motor. How the bearings? Races? Gears?
I have read a case in which a guy built up the transom of his boat (an aluminum utility) in order to use a long shaft OB. Absolutely necessary? Idk...
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