Nissan 5HP doesn't accelerate past 1/2 throttle

[Gi da Joe]

I appreciate any help. It starts easily and runs great up to just past half throttle. Past that it doesn't accelerate, it just sounds like it needs more fuel. I have had the carb rebuilt. The fuel system has been cleaned thoroughly. When running in a test tank past 1/2 throttle I've tried adding fuel through the carb but it runs too rich. When I disconnect the fuel line it will run the same(power loss)at full throttle until it runs out of fuel. I'm at a loss...what do I check now? Could there be an ignition problem?

 

[TOHATSU GURU]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

It's really not likely that you have an ignition problem. It still may be the carb. But, what's your cylinder compression?

 

[jmoser]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Obvious suggestion:<br /><br />You had the carb rebuilt but did you check the throttle linkage? Can you visually see the throttle plate open all the way as you twist the control? Could a cable be kinked or out of adjustment? Maybe you are not really giving it full throttle after all - with the cover off see if you can manually open the throttle linkage all the way.<br /><br />Many carbs are designed to run off the pilot (low speed) jet until 1/2 - 2/3 throttle, then the main jet takes over. If your throttle linkage is adjusted properly and compression is good then I would strongly suggest having another look at the carb with emphasis on main jet / high speed nozzle. Soaking in solvent is not enough - you need to blast out all those passages with compressed air.<br /><br />Check the float level too.<br /><br />BTW - is it a 2 stroke or 4-stroke? How old? Are there any vacuum lines on this engine/carb? If so check for leaks.<br /><br />If you have an ignition problem you should be able to pull the plug and see carbon / fouling / wetness since you will not be igniting the air/fuel charge at full throttle. If the spark plug looks normal then you are probably back to a carb problem.

 

[Gi da Joe]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Thanks for your responses. It is a 4 stroke. The throttle does open fully, the cables work freely.When the carb was rebuilt the main jet and emulsion tube were taken out, soaked, and blown out with compressed air (100 psi). The float level was checked and found to be accurate. The float was checked for proper bouancy. I will check the compression but since it runs well at idle and low speeds i didn't think it would be an issue.<br />Again, thanks!

 

[mjbrueck]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Is this a new problem or did you just acquire the engine? The reason I ask, is if you're running it on a small boat it may only take 2 or 3 hp to get to hull speed but more than 5 hp to plane. In that case, you'd notice very little speed difference between 1/2 throttle and full throttle.

 

[Gi da Joe]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

While pull cranking, the compression is between 85 and 90 p.s.i. I did a cylinder leakdown test and it showed as having less than 5% leakdown. The motor clearly does not run correctly above 1/2 throttle. This is obvious whether running in a test tank or on a boat. It vibrates as though it were slightly misfiring, but evenly, not sporatically.

 

[TOHATSU GURU]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Put an in-line spark checker on it and see if you suffering a spark loss at the problem range. If you are not....then it is a fuel system problem.

 

[mjbrueck]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Are you running it with a test prop or in neutral? I believe it has a rev limiter. If you go past 1/2 throttle in neutral, you'll probably exceed it's max rpms and it will start cutting out. Half throttle under load may be only 2000 or 3000 rpms, but in neutral it could easily be over 6000.<br /><br />I have a tachometer on my motor (9.9 4-stroke Mercury) and once I get around 5500 rpms, my motor behaves just as you describe.

 

[TOHATSU GURU]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

no rev limiter

 

[Gi da Joe]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Well...I got out my Fluke 97A and tested the primary and secondary ignition and found no problems there so I guess it's time to buy a carburetor for it <br />Thanks for all the help!

 

[Gi da Joe]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Anybody have an idea as to where to get a carb for this 1999 NSF5A Nissan 5 HP 4 stroker?

 

[TOHATSU GURU]

Re: Nissan 5HP doesn't accelerate past 1/2 throttle

Any Nissan, Tohatsu or Mercury dealer. They are a little more from a Mercury dealer as they buy it from Tohatsu and have to mark it up a little more.

 

[Sea Rider]

My 1997 nissan 5hp 2 stroke cuts out at high rpms but runs fine at lower rpms. Whenever it cuts out if starts up next pull then it gets to high rpms for a few minutes and then dies again. I think its a carb issue

Better start a new thread on your own or a Moderator will show up..

Happy Boating