low wot rpm's-rodbolt?

[djarrett]

1984 yamaha 150 etln. Chasing a low wot rpm issue, i believe its down about 800-1000 rpm. I read the sticky about how to test your fuel line and bought a fuel pressure/ vaccum gauge. Carbs have been cleaned and it accelerates very smoothly, will idle as long as i want it to. Compression is 100, 105, 100, 103, 100, 102. Fuel pumps have been checked and i replaced one of the diaphrams as it was a little stiff. I did check the screen in the tank for a fuel restriction and it was very clean. The fuel line on the boat is 5/16, as are both outlets on the fuel pumps. Do i need to install 3/8 fuel line before performing the checks or is 5/16 fuel line sufficient for a 150 hp motor? I am very confident this boat came with a smaller motor and someone put a larger motor on it and i want to make sure the fuel line is the correct size. I have a seloc manual and can not find a line size recomendation.

When i first got the boat it would turn about 5100 and i don't know if it would turn any faster, i never tried but now i can only spin about 4400-4600 rpm.



Thanks

 

[rodbolt]

Re: low wot rpm's-rodbolt?

sounds like either you have some dirty carbs again or possibly a line restriction.
8mm lines are what the engine came with.
be aware that the quick connect on the engine side has an oring that can and does swell and can restrict fuel.
we normally remove it and plumb the fuel line straight to the filter.

 

[djarrett]

Re: low wot rpm's-rodbolt?

Well after you said it came with 8mm lines i went back and started checking things again. Thanks for the info, i'll leave 5/16 lines on it. I still need to get the clear lines and barb fittings to hook up my pressure gauge.

So i thought i would check the fuel pumps again since it was the middle of the summer when i last checked them. I definitely found part/all of the problem. Both fuel pumps look like the inside had been filled with saltwater? The springs are covered with rust and the tiny screws and bolts look as they aged 40 years in a few months. The gasket on the bottom pump opposite the spring gasket looks like its been melted and partially dissolved by something. And the bottom pump i could blow both ways thru it and was fult of shrunk looking rubber gaskets and rusted metal hardware also. I don't understand how it got that bad that fast, i use sta-bil every time i get gas. Maybe Ethanol gas on old rubber? Ordered new ones just a little while ago and then i'll test the fuel system pressure.

Rodbolt, i had already by passed the quick connect and filter under the small oil tank because i had read your suggestion previously. I do have a 10 micron fuel water seperator mounted after the gas tank.

 

[rodbolt]

Re: low wot rpm's-rodbolt?

if you had that much trash in the pumps you had best open up the carbs and clean the bowls,main jet and idle fuel jets at a minimum.
junk keeps traveling downstream.
aint this new fuel blend wonderful ??

 

[djarrett]

Re: low wot rpm's-rodbolt?

Ok, will do.

I was wishfully telling myself the carbs will be alright, just went thru them last fall.

But you are right and i will go thru them, hopefully the gaskets won't be in the same shape as the fuel pump gaskets.

Would you happen to have a recommendation for a fuel stabilizer? I do believe i am done with sta-bil, but i am considering the marine formula.

 

[Silvertip]

Re: low wot rpm's-rodbolt?

We've used ethanol blended fuel in the upper midwest since 1997 so it is possible your 1984 engine has some ethanol incompatibility issues with rubber parts. Replace the fuel lines, replace the filter(s), clean the carbs, rebuild the pumps and I will bet your engine comes back to life. Carry a spare filter so you can change it on the water if necessary. Once the fuel system is cleaned up, continued use of SeaFoam will help keep the fuel system clean and it works well with ethanol. It is the "universal" fuel treatment in this neck of the woods.

 

[djarrett]

Re: low wot rpm's-rodbolt?

Alright thanks, but i am also running ring free with the stabil. Sea foam is also a decarb, are you running ring free and sea foam or sea foam only?