Question on 89 Nissan 90hp

[rogerwa]

I just picked my new to me 90 HP Nissan and mounted it to my pontoon boat. Other than the initial problem I had with the idle settings (I think dealer set the idle on muffs not tank), it now idles very well around 900, which I believe is spec, and runs perfect from 1900RPM on up.

My question is that between ~1000RPM and around 1900RPM (I guessing the point at which the butterfly cam is engaged), the motor runs but is very jerky. It doesn't die or lose power, its just that the powerhead is jerky and feels very uncomfortable instead of a smooth increase in power.

The dealer cleaned the carbs before delivery so I am assuming they are clean. Is this the nature of this motor or is there a fine adjustment to make that could help smooth it out..

 

[TOHATSU GURU]

Re: Question on 89 Nissan 90hp

There is a bubble between the slow jet and main jet where you will get a transition bubble, but its around 1650 RPM and only affects the RPM in a 50 RPM range. A 900 RPM range indicates some kind of problem.

 

[rogerwa]

Re: Question on 89 Nissan 90hp

I do not yet have a manual on this motor, but is the slow speed jet different from the idle circuit that is adjustable? If so, is the slow speed jet just a passage in the carb that could have been missed in their cleaning. The behavior does peak around the middle of the range, which would support your bubble argument, I am just wondering if I am getting inconsistent fuel delivery across the three carbs in that range.

 

[TOHATSU GURU]

Re: Question on 89 Nissan 90hp

The slow speed jet is a jet so it is not adjustable. I think you are referring to the air mixture screws or the idle adjustment screws. The problem might be limited to one carb, probably is, and you just need to re-clean the carbs.