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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.