nissan 90 A????

[hamegg3]

nissan 90a runs great but surges at wot. have seen other threads with suggestions on checking fuel delivery and some on pulling flywheel and cleaning/ checking ignition system. any advice on solutions for this particular problem on this particular motor????????

 

[hamegg3]

Re: nissan 90 A????

just had carbs built at nissan dealership. only goes to 4500 rpms

 

[rogerwa]

Re: nissan 90 A????

GIve it time.. Not a whole lot of action here on the Nissans and Tohatsu. I am a new owner of a 90A myself and just getting to know it..

Maybe a better description of what is happening would be a good start.

When you say surging, do that mean the the RPM is going higher that the normal RPM for brief periods or does it mean that it dips. Different thinking would go into each of these answers.

If it is dipping, then I would carefully evaluate the fuel lines in front of the pump for leaks. It can suck air and that would cause a kind of undualting RPM.

If this is surgin over the normal RPM, then are you having issues with ventilation or the prop??

Again a little more detail will help.

 

[hamegg3]

Re: nissan 90 A????

thanks so much for the response!!!! the rpms only get to about 4500 and then it dropps surges from there. i have never been above 4500 rpm. just had carbs built and problem was same before rebuild. thanks again for your time!!!!

 

[hamegg3]

Re: nissan 90 A????

i would say it is dipping as you describe it. i will check for sucking air problem before pulling the flywheel. is pulling fw a good idea on an older engine to clean. probably has never been done.

 

[rogerwa]

Re: nissan 90 A????

Look at fuel delivery. First look for air leaks before the fuel pump. Check tank pickup for obstuction. Ensure the vent is unobstructed and fully open. Pull fuel filter and check for contamination. From there you can look at your fuel pump. I believe this has a diaphram that could have developed pin holes.

I am not sure why you would pull your flywheel . What is under there would have more to do with timing than anything.

Did this problem just start or has it done it all along.

Also, you are not propped correctly. You should be running 5000-5500 RPM.

 

[hamegg3]

Re: nissan 90 A????

thanks rodgerwa, I assumed because of the problems at wot (surging, dropping) , that maybe i was not achieving 5500 because of that. I will check and see what wot rpms are after trouble shooting the surging/ dropping problem. you may be right-o. dont know if this is original prop oR MAYBE its not propped right for the boat i put this engine on.

 

[TOHATSU GURU]

Re: nissan 90 A????

Check your trigger coils. Surging, with regularity, is usually electrical