Nissan NS40C “missing” getting up on plane after idling

[kowached]

Hello, this is my first post, thanks for taking the time to read this.<br /><br />I’ve had a consistent problem with my Nissan NS40C since I purchased it used 3 years ago. The Nissan was part of an Avon 4 Meter Rigid-hull Inflatable Boat (RIB) that is equipped with remote steering and throttle, battery start, electric choke.<br /><br />The Problem: Every time I idle down the canal (15 minutes of no wake) before I get to open water, the Nissan chokes and sputters when I try to the boat up on plane. If I only have two people on board, she’ll eventually get up and go, but with 3 people (or a heavy cooler) she might never get up, even after a couple rev’s in Neutral to clear up excess fuel. Once she is up on plane, the Nissan runs strong, 32 MPH strong. I can usually set the boat down and if I get back in to the throttle quickly, I can get right back on plane with no choking or sputtering.<br /><br />What I’ve tried: <br /><br />At first I thought the mass in the electric choke system was causing the choke butterfly to close under acceleration, so I removed the actuator and made sure the spring was good and stiff. No change.<br /><br />I was running Amsoil synthetic 2-cycle oil, then switched back to the Nissan stuff. No change. I always measure 50:1.<br /><br />I was running premium (93 Octane), then it was suggested that the premium has a higher resistance to combustion (anti-knock index), so I dropped down to Mid-grade (89 Octane). No change.<br /><br />I replaced all the old fuel lines, and fuel filter. No change.<br /><br />New carb gaskets and fuel bowl float. New Pilot Screw. Cleaned every air hole/jet. No change.<br /><br />Countless spark plugs. No change.<br /><br />It seems like excess fuel is loading up in the engine, but I would think that the excess fuel would cause uncontrollable RPM increase at idle, no?<br /><br />Questions:<br /><br />1. Pilot Screw: From the lightly seated (all the way in) position, how many turn out is a good place to start? What type of adjustments do I make from there? I have the factory manual, buts it is not so useful here.<br /><br />2. Is it possible that there is a malfunction with the main jet, main air jet or main nozzle causing excess fuel to be dumped in at idle?<br /><br />3. Maybe its time for a new slow air jet and slow jet?<br /><br />4. Is it time for all new jets?<br /><br />5. Heck maybe a rebuilt carb? Any favorite Nissan sources?<br /><br />I think that the Nissan is a quality motor, but this problem has been driving me crazy for far too long.<br /><br />Thank you,<br />Dave

 

[John_S]

Re: Nissan NS40C “missing” getting up on plane after idling

I have an 80's Nissan 40hp twin. Not sure if it is a "C" or if that is for the three cyl model. Also have a 90's 18 hp twin 2 cyle. Both were purchased new, and both have the issue you describe, but to a lessor degree than what you have. I have done some of what you have tried, as well, but same results. I believe it is just oil fowling of the plugs from long idling. I seem to get it worse when running the engine tilted for shallow water protection. The only times I haven't been able to get it cleaned out by running, has been when the plugs needed changing. I have not tried running one step hotter plugs. Need to be careful with hotter plugs. Long wide open runs might burn a hole in pistons. Otherwise, these motors have been excellent performers, and have held up very well. Better than the small Johnson/Evenrudes I've owned.

 

[phatmanmike]

Re: Nissan NS40C “missing” getting up on plane after idling

i agree with john, i own 3 nissans and they do hold up very well, better than my omc's. i own 9 motors, and besides my big "tower of power" merc 1150 inline 6, i love my nissans the most.<br /><br />it sounds like you could use a "decarb". its cheap and easy, only cost 8 bucks... do a search on decarb here, youll find tons of info.<br /><br />also sounds to be fuel related. how is your fuel pump? when was last time carbs were rebuilt and cleaned? is your ign timing adjustable? if so is it set right? but try the decarb first, its the easiest<br /><br />m ikey

 

[caveguy]

Re: Nissan NS40C “missing” getting up on plane after idling

Originally posted by kowached:<br /> Hello, this is my first post, thanks for taking the time to read this.<br /><br />I’ve had a consistent problem with my Nissan NS40C since I purchased it used 3 years ago. The Nissan was part of an Avon 4 Meter Rigid-hull Inflatable Boat (RIB) that is equipped with remote steering and throttle, battery start, electric choke.<br /><br />The Problem: Every time I idle down the canal (15 minutes of no wake) before I get to open water, the Nissan chokes and sputters when I try to the boat up on plane. If I only have two people on board, she’ll eventually get up and go, but with 3 people (or a heavy cooler) she might never get up, even after a couple rev’s in Neutral to clear up excess fuel. Once she is up on plane, the Nissan runs strong, 32 MPH strong. I can usually set the boat down and if I get back in to the throttle quickly, I can get right back on plane with no choking or sputtering.<br /><br />What I’ve tried: <br /><br />At first I thought the mass in the electric choke system was causing the choke butterfly to close under acceleration, so I removed the actuator and made sure the spring was good and stiff. No change.<br /><br />I was running Amsoil synthetic 2-cycle oil, then switched back to the Nissan stuff. No change. I always measure 50:1.<br /><br />I was running premium (93 Octane), then it was suggested that the premium has a higher resistance to combustion (anti-knock index), so I dropped down to Mid-grade (89 Octane). No change.<br /><br />I replaced all the old fuel lines, and fuel filter. No change.<br /><br />New carb gaskets and fuel bowl float. New Pilot Screw. Cleaned every air hole/jet. No change.<br /><br />Countless spark plugs. No change.<br /><br />It seems like excess fuel is loading up in the engine, but I would think that the excess fuel would cause uncontrollable RPM increase at idle, no?<br /><br />Questions:<br /><br />1. Pilot Screw: From the lightly seated (all the way in) position, how many turn out is a good place to start? What type of adjustments do I make from there? I have the factory manual, buts it is not so useful here.<br /><br />2. Is it possible that there is a malfunction with the main jet, main air jet or main nozzle causing excess fuel to be dumped in at idle?<br /><br />3. Maybe its time for a new slow air jet and slow jet?<br /><br />4. Is it time for all new jets?<br /><br />5. Heck maybe a rebuilt carb? Any favorite Nissan sources?<br /><br />I think that the Nissan is a quality motor, but this problem has been driving me crazy for far too long.<br /><br />Thank you,<br />Dave

 

[caveguy]

Re: Nissan NS40C “missing” getting up on plane after idling

I have a 92 Nissan 60 HP twin. It was doing much the same thing (acted even worse when warmed up).<br />A torn diaphram in the fuel pump was the problem.<br />This was allowing excess fuel to leak past into the crank case through the pulser passageway. The leak was small enough to still permit the pump to deliver enough fuel to the carbs at high revs where the extra rich mix had little effect, but at low revs and especially at idle, the extra fuel was more than enough to flood one cylinder and eventually foul its plug to the point where it died on that cylinder. When the engine was still cold it was not nearly as bad (a cold engine needs a rich mixture anyway-the choke normally does that).<br />Apparently just because the pump was putting out a good supply of fuel did not mean that all was well inside of it.