Nissan/Tohatsu 9.8 high to low altitude

[montenido]

Think about the prop when changing altitudes. I use a ski boat at 7000 feet and need a different prop than at sea level. The 175 Mercury OB runs fine at both elevations, but needs to spin more easily at high altitude. Without the prop change, the boat just bogs and can't pull a skier. I would think the same applies to a smaller motor.

Ask your OB dealer.

My $.02

[TohatsuGuru]

Working my way through the posts in order:

Changing "the jet" will not do anything as you have to change both jets for each elevation range:

InternetOutboards.com - High Altitude Jet Kit, 6600 Feet, Nissan/Tohatsu, 4-Stroke, 9.8 hp, All Models, FREE SHIPPING

InternetOutboards.com - High Altitude Jet Kit, 3300 Feet, Nissan/Tohatsu, 4-Stroke, 9.8 hp, All Models, FREE SHIPPING

It's a must do as the power loss is about 50% at 9000 feet. Even changing them out with the above kit your still going to lose a little at anything above 8000. Smart money says change them out for each specific elevation or lose power even though its a pain. Conversely, changing them out for elevation and then running them back at a reduced height is an extremely bad idea. Think in terms of metallic dispersion in an energetic manner bad. You must change them back or the term "lean" will come complete with an audio from your engine as the thing begins to sound like nails on a chalk board. That's an exaggeration of course But, you get the point.

The 1-17 screw is an idle speed adjustment screw and does not make the engine rich or lean. EPA requirements in the U.S. require "fixed" settings so engines are no longer able to be legally tweaked that way....There is a hidden mixture screw, but you do not want to drill your carb to get to it as you could not adjust it enough to make a difference for altitude.

With the proposed 15% alcohol dilution for fuel in the works and the proposed catalytic converters requirement in the works things are going to become very dicey for outboards over the next five years. Alcohol, at 10%, is already pushing the envelope as far as outboards are concerned. Running lean, as alcohol content increases, will be an issue.

Dropping the prop pitch isn't a bad idea, but it can't make up that kind of difference on a simple, small outboard. Larger, smarter engine's with Hal 2000 ECU's can vary the settings by themselves and compensate for a lot, but the usually limit is about 4000 feet and then you start wondering why you can't pull your fat a@@ brother-in-law up on skis anymore

[pedcab]

And that's it. I'm humbled by your comments I really thought the 1-17 screw was a mix adjustment, at least it seems to behave like one in my 199something Tohatsu 5, for idle speed adjustment I've always used the throtlle stopper screw... What am I missing here? Can motors sold in Portugal be different from those being sold in the States?

About the overheating when running lean, I've managed to inform myself better and I owe an apology. Apparently, due to the reduced flash point of a leaner mixture, engines will overheat if running on roughly leaned out mixture. Nevertheless if an engine is forced to run on such poor mixture that it can cause damage to it the operator will probably notice loss of power and early ignition symptoms...

Am I right?

[TohatsuGuru]

Actually engines sold in the EU do have different carburetors than the ones sold here as they have different emission requirements. Also, older model engines did have air mixture screws.

[pedcab]

So that's the story... What a relief Because I am really pretty sure that my carb does have a perfectly acessible mix screw and I was beginning to think I had dreamt it ...

Thanks for the explanations!

By the way, this is my engine:



Regards!

[tommays]

And for good measure theres a lot of California only stuff that has a bad habbit of becoming the rule for USA motors

[TohatsuGuru]

CARB ....CRAP. There's only one letter difference

[waltsn]

Much thanks to everyone for all the reply's on this (and the other) Nissan/Tohatsu thread. Very useful to me!!!