ns90a engine rev = low/loss of power

[Bigfella73099]

I am helping a friend with his 24' pontoon. He has a ns90a motor. I am not sure of the year. The boat is a 91', so I am assuming a 89' or 92'. I have read that the year isn't as important as the serial number.

The motor has a few problems the first is a warning tone when it is first put into gear. When you give it more throtle the tone goes away. From reading the forum I have deduced that this could be low flow water supply. (there is plenty of oil) Where should I start checking for clogs?

Another problem it has it that has really low power. We were giving it all we could and got passed by a 22' with a 40hp OB. I am plan on looking at the prop to see what the pitch is, but I think we are a long way from where we should be in regards to the amout of power we should see.

This might be related to the lack of power, but when we give it full throtle we lose prime? I am not sure if that is the way to say it. The engine revs and we lose all forward thrust. If we pull the throtle all the way back and slow down we can ease back into the throtle and gain forward thrust again.

We did replace the spark plugs, altough they didn't look terrible.

Any help is appreciated. Thanks in advance!

 

[jlams73]

Re: ns90a engine rev = low/loss of power

If your engine RPM goes up but the speed fluctuates then it sounds like you have a spun hub. I would take the prop off and inspect the hub for damage.

 

[Bigfella73099]

Re: ns90a engine rev = low/loss of power

Thanks, I will take a look at that when we can get down to the boat.

 

[pvanv]

Re: ns90a engine rev = low/loss of power

Probably a spun prop hub. You can get a new one from any Nissan/Tohatsu dealer, including me... and iBoats has a few as well. The factory prop selector chart is available at http://www.nissanmarine.com/accessories/prop_chart.html The alarm buzzer shouldn't be ignored. For a description of the warning conditions, d/l a copy of your owner's manual at http://www.nissanmarine.com/tech_talk/owners_manuals.html and review p62. You may be low on oil, or the water cooling may be poor. Is the telltale squirting? If not, you may need a water pump kit. The alarm condition for the 90A will also limit RPM to about 3500, so if the prop is OK, once you fix whatever is triggering the alarm, you should again be able to go full speed.