Yamaha 115 4 stroke loss of power

[angjackson29]

My yami 115 4 stroke has loss top end power and sounds bogged down. From what I have read could be Sreen in VST tank. Has anyone ever proformed
this task? I know intake manifold has to be removed too get to it.
Ang

 

[rodbolt]

Re: Yamaha 115 4 stroke loss of power

nope, never seen one before.
a model number would be nice
make sure you update the inline filter between the lift pump and the VST to the new 10 micron one while your in it.

 

[nova23zz502]

Re: Yamaha 115 4 stroke loss of power

I see this is an old thread but I have an older Friend who needs help with same engine. 2001 115hp four stroke saltwater series fuel injected. Has a 2000 year primer pump on cam shaft side of engine. Bogs @ 2000 plus rpm's. If I add artificial fuel, she will take off and then back to a bog when artificial is taken away. I have a bad feeling it is the high pressure pump. New plugs, not fixed, Fuel filters, not fixed, Pulled vac hose off regulator,no change, Pinched fuel return line from rail, no change. Timing belt 2.5 years old looks correct and still new. Also suspect first generation diaphram primmer pump. I am goin to do a fuel pressure test soon, did not have my equipment down beach yet. Any body know what my Pressures should be at idle and on the throttle?? I am also going to By-Pass boats fuel system Completly with a small tank and & 7 psi pump.

 

[nova23zz502]

Re: Yamaha 115 4 stroke loss of power

I think I am heading towards VST in pump filter behind intake.

 

[rodbolt]

Re: Yamaha 115 4 stroke loss of power

if the fuel pump diaphram isnt broken and leaking gas into the oil pan dont sweat it.
if the fuel pump starts sounding like a bad lifter in an old chevy look for fuel restrictions or airleaks from the tank liquid level and the ful pump inlet.
if it runs at all the HP pump is good 99% of the time.
look at the rail pressure, a clogged VST filter can and will crate that problem as can a cogged filter between the mechanical pump and the VST,if used. if not install the 10 micron inline on reassembly.
the VST filter is on the HP pump inlet and is about the size of a pencil eraser.
quit splatter gunning, you verified its fuel why play with plugs and such?

 

[nova23zz502]

Re: Yamaha 115 4 stroke loss of power

I just came onto the job owner and his son did previous work. I diagnois not guess always.

 

[rodbolt]

Re: Yamaha 115 4 stroke loss of power

your not diagnosing cause you have not posted secondary Kv voltages,primary peak voltages or fuel rail pressures.
low pressure fuel should be about 5 PSI and high pressure fuel about 34 to 38 PSI at all RPM ranges.