Nissan NSF 9.9b Idels great, no pwer at higher rpm and acts like it is missing

[WOTJunkie]

I have a 2001 Nissan nsf9.9b. Tiller and rope pull. Idles great in barrel and on sea trials. Giving 50% or more throttle starts acting like it is miss firing or fuel mixture is off. Mixture screw is about 1.5 turns out, turned in till it starts to cut out then out 1. But that is not the problem. Carb completely soaked cleaned blown out etc. Put it back together and same story. Good spark. New plugs. Clean fuel and new lines. Compression test shows 65lbs per cyl. Will idle fine all day. Under load does ok up to about 30% throttle then starts spitting and sputtering never really revving up like it should. It will run WOT but like crap, and no where near full rpm.
Ideas, suggestions, next steps?

 

[Sea Rider]

Welcome to Iboats,

Compression should be 114 PSI, don't know how many Lbs that would be ? Those symptoms could be just anything from a spun prop with a combination of electrical issues when all electrical components heats up and misses to a faulty head gasket issue. Mixture screw is just for idle speed, put it back to factory specs.

Happy Boating

 

[pvanv]

When did these symptoms start? What do the plugs look like when this happens? The pilot screw should not be adjusted, but if you did, put it back where it was. Run the ignition tests in the Factory service manual, and check for a spun prop as Luis suggested. Also verify proper operation of the ABS solenoid.

 

[JDusza]

Not very familiar with the engine but there are a couple things you can do to sort things out. Is it a 2 or 4 stroke?
Not sure a spun prop would make the engine falter as described. I would think a spun prop would give over-revving.
How did you check spark? Be sure both cylinders are firing by removing one spark plug wire at a time. If the engine falters, then the cylinder was working. If the engine doesn't falter then the cylinder is not firing.
Check fuel delivery by pumping the squeeze ball when the engine falters. If the engine begins to run smooth, then you are starving for fuel under demand and have a fuel delivery problem. If no change, then may indicate an ignition or ignition advance issue.
J

 

[pvanv]

It's a 4-stroke. It has starting decompression, so 65 is fine. Ignition advance is programmed into the CD, so it's not adjustable. Verify fuel delivery and ABS, as well as the prop hub, and test the ignition, using an analog (not digital) ohm meter.

 

[WOTJunkie]

Thanks everyone for your replies. Let me address each suggestion. Fuel delivery does not seem to be the issue. The fuel pump is working, the bulb stays pumped up and squeezing while giving the engine throttle does not make a difference. I have a clear fuel filter and I can see the fuel flowing as expected with no sign of air entering the fuel delivery or signs of the motor starving. ABS is also working, when 12 volts is applied. I can have watched the unit function off the carb. It also starts pretty easy when cold. Both plugs have blue spark when I test them with a spark plug. I do not know how to test if the CD Ignition unit is failing at higher rpms. Not sure when it started, ran the engine a few times and it ran great, then this issue started. Also not sure how the prop hub figures in it since will spit sputter and hesitate on the hose or in a barrel even when not in gear. Happens at about 50% throttle or more. I will try the remove a plug wire test today, and verify the fuel delivery is not an issue. Thanks again, my little boy wants to go fishing. Confused

 

[Sea Rider]

Is carb butterfly working properly, that's fully closing when engine is cold, fully opening when engine is warm, or get's stuck at some point between cold and warm ?

Heat ups on any electrical component is the worst time demanding to diagnose fast and properly. One thing is testing on a barrel or on muffs, other story once on water at load. You could have a simple Ignition Coil issue that starts to fail as soon starts heating up. On those cases the fastest way to detect truoble is a IC swap and a water test under load. It's good to have a spare IC. Spun prop could be checked latter once engine is running at top state. If it were me, would buy a spare IC, swap and test at load.

Happy Boating

 

[pvanv]

Whip out your trusty Factory service manual and use it as a guide to dx the ignition system when warm, using an analog (not digital) ohm meter. That can tell you a lot.

 

[Sea Rider]

Buying a Factory Service Manual and a Special Analog Meter to troubleshoot electrical components will outcost the price of a new OEM IC. When electrical components are KO, kaput, it's much easier to detect each electrical component failure, but when missing due to intermitent internal overheat, shorting of some kind, it's other long story, testing to spot those failure conditions on water with cowl removed while boating is a PITA.

Happy Boating

 

[TOHATSU GURU]

Go back to the carb and clean it again. Your symptoms indicate a fuel system issue. You may also be having a fuel starvation problem even though the bulb is hard. Drop the money for the manual if you want to be able to test the ignition system.

 

[WOTJunkie]

Ok. Great advice from everyone. I checked for spark leak, at night none. Pull one plug at a time engine wanted to die equally as bad for either plug. Talked to the local Nissan mechanic he seems to think it may be running as designed and I am hearing the rev limiter kicking in. My gut tells me the carb is still not right. Acts like it is starving or a clogged jet. Took the carb completely apart and hand cleaned it every nook and cranny, soaked it for 4 hours in carb soak, blew it out, rinsed with carb cleaner and reassembled. Still the same performance. Float and needle valve look good. Jets are clean as a whistle. Accelerator pump or what ever is in good shape and so is the rubber plunger thing. Just bought the entire replacement ignition system from a good running motor with bad lower end. Will start part swapping and post my results.

 

[Sea Rider]

If your mech is right and rev limiter is kicking in prematurely, that's why engine misses when giving full juice. All what's posted here ir irrelevant. If engine is used on a very light application you're over revving, seems you have still more throttle to go. To retard premature kicking will need to go for a 1+ prop pitch to lower rpm down and to have more throttle to go. Will need to install an induction tach and check at which rpm the engine is kicking in, then go from there for a prop maximization.

Happy Boating

 

[WOTJunkie]

Ok, if it is the rev limiter, it must be going bad and kicking in prematurely and will need to be replaced, right? It shows this behavior in the barrel or on the water, in gear or in neutral. Since I do not have a special outboard tach and I am not familiar enough with this motor, I cant say if it is over revving. But a broken or malfunctioning rev limiter would precisely describe the behavior I am seeing. The new prop and ignition components are on their way, again will post my results as soon as I get them. I went with the factory size 9.25 dia, 9 pitch, 3 blade and stainless. Thanks again, really appreciate all the feedback.

 

[pvanv]

What is your oil level on the dipstick?

 

[Sea Rider]

Being 4 strokes not my favorite ones, assume Rev limiter is located on ECU, will need to change complete ECU if it's a ECU misbehavior or missing. If you have Ignition Coil on its way, try it, that's probably the direct culprit. Good Luck.

Happy Boating

 

[WOTJunkie]

Well turns out it was the Carb and the prop combination. Never even touched the coil or ECU. (Have them as spares now). Switched to a larger prop and took it out, runs perfect and fast. Thanks to everyone. My sons got to catch a boat full of fish this weekend. That rev limited messed me up, making me thing it was missing. This is a great community that really helped me out.