Losing Power

[BassNBob]

I seam to be losing power on my 2000 Nissan 25HP as the day progresses. What should the compression be on this motor or do I have other problems?

 

[Quackrstackr]

If it was a compression issue, it shouldn't be a cyclical loss of power. Once it was gone, it should be gone.

Most outboard motors are sensitive to temperature changes. The performance of mine is down quite a bit right now from what it is when the air and water temps are cooler.

https://www.marinepartsman.com/how-weather-affects-outboard-and-marine-engine-performance.html

The more load there is on a smaller motor, the more that may show up in the daily temperature swing.

Just a thought. That's the only thing that I can think would make a loss of power as the day progresses.

 

[Zum]

Is it losing power or rpm...both?
Can you get your top rpm at the end of the day?
If not maybe a bad diaphram in fuel pump,bad line or gas hose

 

[BassNBob]

It is at WOT in the morning and later in the day coming back to the ramp it is WOT. I have no way of checking compression or RPMs.
I hope this answers your question.

 

[SlimeTime]

Couple of silly questions (but ya never know unless ya ask)....you sure you've got the proper oil/gas mix? And you open the vent on the tank prior to firing the motor initially?

Grab a can of SeaFoam & mix (according to directions) into your fuel, can't hurt. :wink:

EDIT: Do you usually bring-in 2-300 pounds of fish at the end of the day? That'd do it :mrgreen:


ST

 

[BassNBob]

Brand new gas tank with new gas mixed 50:1. Oil measured from a measuring cup. Bulb hard, vent open.
Runs good at idle and can troll at that speed if needed.

 

[SlimeTime]

It would be hard to say.....without knowing for sure you have a problem. Do you have a FF that reads speed? If so, you could get a WOT speed early in the day, as well as later on. I know sometimes my mind does funny things.....it sounds like you're "problem" is so slight, you're really not even sure you have a problem.

I'd look under the cover for gas/oil stains, and give it a shot of SeaFoam & as long as everything sounded good, and you don't have something noticeable, I wouldn't worry about it.

I'm assuming it's pumping water good? May want to replace your impeller sometime, just to know it's been done & is good.

ST

 

[Zum]

If your at WOT at the start of the and WOT at the end of the day,maybe your "power"lose is at the prop....spun hub?

I don't think it's that though

 

[Quackrstackr]

I'm still sticking by my heat/humidity of the day knocking off the performance of a smaller engine diagnosis. :wink:

What boat/configuration do you have this motor on?

 

[BassNBob]

I had a new water pump put on last Friday and checked it out again last night with water muffs. Peeing good with pressure out of the engine.
The speed is being measured by my gps on the boat. It went from 19mph in the morning to 16mph at 11:00 coming back in to the ramp with very little wind. Very little water in the bottom.
It must be the temp. and humidity.
Thanks all for the info.

 

[BassNBob]

Zum, what causes a spun hub?

 

[Zum]

A spun hub is when the rubber around the splines in your prop let go.It can happen if you hit something but also sometimes just from old age,there rubber dryrot I guess.
I don't think yours is that because it goes good in the morning and then goes bad,unless maybe it holds for awhile then starts to let go.Your rpms would still go up but you wouldn't get the normal speed.They normally go real bad though and you can't get above 10mph without the rpms going way up.
Maybe try taking the cowling off and run it,see if that makes a difference.

 

[Popeye]

Lake or river? Any current?

 

[BassNBob]

Lake