15 hp Nissan idle problems

[laguna80]

Hey all, I have a 15 HP Nissan outboard with external fuel tank (model # NS15B2) that is having some problems. Number 1: On start up, the engine revs really high on its own. Choke is pushed in while running. I have the tiller handle at the start position and it does this when it's cold and warmed up. This is easily adjusted down by moving the throttle to the "turtle" position. However, the engine speed increases dramatically if returned to the start position or beyond that to the "hare" position. Number 2: the engine will not idle at the proper speed. Once it drops down to a certain point, the engine dies out. So far, I have adjusted the idle speed screw so that the engine will stay running, but it is not the proper idle speed of 600-700 rpm. The engine also tends to die out, if it's at a lower speed and the engine is put into forward or reverse. It won't die if the engine is revving higher and then it's put into forward or reverse. Number 3: This only happens on occasion. The engine will conk out randomly while operating it on plane. Not going full throttle, probably about 60% of that. Generally, it is more difficult to start after this happens. Anyone have any ideas? I'd be happy to post video if that would help. Thanks!

 

[TOHATSU GURU]

Re: 15 hp Nissan idle problems

Fubard carb. With no parts being available for it you may be screwed. Clean it correctly and try it again.

 

[laguna80]

Re: 15 hp Nissan idle problems

I was afraid of that. My dad (it's his motor) already paid someone who said they cleaned the carb. I'm guessing they took the 100 and ran. I'll try to find the FSM online or something. I have carb experience (course that's with old 70's landcruisers). Thanks for the reply.

 

[MJS]

Re: 15 hp Nissan idle problems

My 18 Nissan may be different but was having similar problems and there is a mixture screw hidden by a plug that needed to be drilled to expose he screw and adjust mixture. That fixed mine after a carb cleaning failed.

 

[laguna80]

Re: 15 hp Nissan idle problems

Is yours a 2 stroke or 4 stroke? I've had to do that with an old landcruiser before. Still trying to find the FSM. Where is that screw located on your motor? I'll see if there is a similar one on mine.

 

[pvanv]

Re: 15 hp Nissan idle problems

My 18 Nissan may be different but was having similar problems and there is a mixture screw hidden by a plug that needed to be drilled to expose he screw and adjust mixture. That fixed mine after a carb cleaning failed.

He does not have that. Yours is a modern 4-st.

 

[pvanv]

Re: 15 hp Nissan idle problems

Is yours a 2 stroke or 4 stroke? I've had to do that with an old landcruiser before. Still trying to find the FSM. Where is that screw located on your motor? I'll see if there is a similar one on mine.

The factory service manual is copyrighted, so not available online. But contact any dealer (including me), and we can sell you the book.

 

[laguna80]

Re: 15 hp Nissan idle problems

Thanks!

 

[MJS]

Re: 15 hp Nissan idle problems

Mines a 2009 4 stroke

 

[TOHATSU GURU]

Re: 15 hp Nissan idle problems

MJS,

The hidden air mixture screw did not need to be adjusted. Basically your mechanic did not know how to clean the carb correctly and rather than re-do it, he compensated for it by unnecessarily enriching it. Now you use a little more fuel than you need to so every time you by gas for the engine you should send him a bill for the extra dollars worth of fuel you use And yes, I am exaggerating.

 

[laguna80]

Re: 15 hp Nissan idle problems

Carb has been disassembled, cleaned and reassembled. Can the fuel filter be taken apart and cleaned as well? I have it removed and I can see a lot of junk in there, but can't get the clear cup part to detach from the intake/outake portion. Does it just unscrew?

 

[laguna80]

Re: 15 hp Nissan idle problems

Nevermind...just needed a little elbow grease. In any case, the problem is still there. Below a certain point on the turtle, the engine dies on its own and above that point the engine revs higher on its own. I haven't let it rev too high because I don't want to damage the engine. The carb appeared spotless when I took it apart. Is there anything I can do to fix this?

 

[pvanv]

Re: 15 hp Nissan idle problems

Sounds like the idle passage is still varnished. What method did you use to clean the carb? If you did not submerge it in real carb dip (such as Tyme) for 4 hours, followed by a blow-out with generic carb spray, you need to do that.

Did you remove the jets and the emulsion tube nozzle when disassembling? (that must be done when disassembling for the bath in the dip.)

What setting (number of turns) is the idle mixture pilot screw adjusted to? When you reassemble, that should start at about 1-3/4 turns out, and then be adjusted as per the Factory service manual.

Is the float parallel to the carb casting when inverted? If not, that must be corrected. When you disassembled the integral fuel pump section, did you verify the condition of the check valves and diaphragms?

Also, you can get new filter elements for the settling-bowl type filter (that was used on the 15B2), or you can use the modern "disposable" type filter if your old one is damaged/leaking.

 

[laguna80]

Re: 15 hp Nissan idle problems

Ah I didn't go into that great a detail. Just did a generic disassembly. I'll go ahead with the full on one. Thanks for the help!

 

[laguna80]

Re: 15 hp Nissan idle problems

Out of curiosity, since a rebuild kit isn't available anymore, how bad is it to use the old parts?

 

[TOHATSU GURU]

Re: 15 hp Nissan idle problems

It works like this. Replacing good parts with good parts will result in zero change. If you have a bad part and you don't change it out, you have zero change.

 

[laguna80]

Re: 15 hp Nissan idle problems

So, there is a bad component to the carb you think? I doesn't just need a cleaning?

 

[TOHATSU GURU]

Re: 15 hp Nissan idle problems

Don't know. You probably need a new inlet needle and since one is not available the engine is going to be a static display. The idea is not to just randomly replace parts. Inspection of the carb will determine what, if anything, that actually needs to be replaced.

 

[laguna80]

Re: 15 hp Nissan idle problems

Thanks for the replies, I learned a little history about the motor and that it had been sitting for quite some time before being given to my father. That's too bad the parts aren't available anymore. It'd be a good motor to have. 15 hp can take us anywhere we want to go on the California coast. As it stands, we'll gonna sell it for parts or trade in and get a ~10 hp motor, one that's a tad lighter and newer, so parts will be available. Thanks for all the help everyone. Truly appreciated.

 

[Sea Rider]

Re: 15 hp Nissan idle problems

That horse idles at 800 in gear, 950 at neutral, not 600-700 too low, engine generally drops dead, adjust if needed. If engine still having problems after last carb dip clean, sometimes connector ends are the cause, internal o'rings wores out/dries and lets small air bubbless pass to carb. Could buy them at auto shops as Tohatsu does not sells them as spares.

Happy Boating