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Nissan 2-stroke 70 hp idle air adjustment

JD Hunter

New member
Nissan 2-stroke 70 hp idle air adjustment: embarrassing question.

The little screws on rh side of carb body near the top & towards the back, the idle air adjustment screws. I've flat forgotten how many turns open, from closed, should they be. It's a three cylinder engine and when idling there's virtually no change if only one of the three is turned either way.

By the way, a few years ago this engine replaced a much older two cylinder Tohatsu of same rated 70 hp. The old Two-hatsu was a great engine that probly ran 5000 hours but I gotta tell ya this Nissan romps! Immense authority!
 
Wow! That was totally fast! Thank you very much. That sounds a lot like what I was told years ago. I've had these carbs all apart putting in new floats & valves last year. Unnecessarily. It turned out the real problem was the pump diaphragm cracked in an arc alround the flex line. It resembled a sheet of polyester Mylar drafting film, not like the reinforced rubber I'd always seen in that aplication before. The replacement looked like rubber and is working fine. I wondered if Nissan was trying out something strange that didn't work well? You know anything about that?

Anyway, of course the idle air screws were all removed and for the life of me I just couldn't remember the magic setting. Judging by the passageways through the castings it looks like fuel from the bowl would be going thru the tunnel the screw points are metering. Can you describe the operation of those screws or point to a good diagram? Traditional outboard mechanics don't hold many mysteries for me but this is one.

Really, thank you again.
 
The idle mixture screws are set to meter the fuel as you mentioned. The NS70C carbs should be synchronized, and the carb assembly likewise synced to the ignition. Full details are in the factory service manual, Part # 003-21036-1, $44.17, available from any dealer, including me.
 
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