fuel supply side "vacuum" question

[fairdeal]

for many years, the "Yamaha Rigging Guide" document included this section

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and later on the page this:



Putting aside the possible confusion in sementics
(does one lower the pressure? or increase the vacuum?)
and Boscoe's stance that there is no such thing as vacuum anyway
(I think that is what he has expressed)


I think we know what Yamaha means here.

The point I am raising: I don't believe them


Why would a "larger filter" be more restrictive to flow ?

with a larger surface area of the same type/porosity of filter media

I would expect a larger filter to - if anything -

have less resistance for the same volume of liquid movement

[boscoe99]

What is "vacuum pressure"?

There is pressure. More pressure or less pressure. Less pressure all the way down to zero pressure. More pressure as far as infinity.

Boscoe does not like the use of the word "vaccum". Well, maybe in a vacuum cleaner it is OK but not for a motor. What some will call an engine.

Yamaha places their fuel pumps downstream from the fuel filter. Such that the pump has to do more work. Sometimes Yamaha has to use two or three mechanical fuel pumps to get the job done.

Mercury places the filter after the fuel pump. Generally only one fuel pump is needed to do the job.

Based on the way the fuel system is designed in a Yamaha there is a concern with respect to fuel starvation. Adding any additional fuel filtration causes the restriction to fuel flow to rise. I suspect that once upon a time Yamaha did not want a boat mounted filter installed. Once they realized the one on the motor was insufficient for the task at hand they started endorsing boat mounted filters. And then cautioned their mechanics to be sure there was still sufficient fuel flow to the motor.

[oldmako69]

All this makes depresses me horribly. I have insufficient suction both at home and at the dock. But, my problematic Port motor seems to now be sublime. Sweet!

Wailing on suction / vacuum issues on the other one. I think that a clogged (or, pinched?) VST vent line might be the culprit. That and a Low PSI pump that doesn't want to run. Is there a stand alone relay for this mother or is it totally within the ECU?

This tequila is great, BTW.

[fairdeal]

I think that a clogged (or, pinched?) VST vent line might be the culprit. That and a Low PSI pump that doesn't want to run. Is there a stand alone relay for this mother or is it totally within the ECU?

There is a relay - yamaha calls it a "driver"
the ECU grounds the relay to actuate, which grounds the pump to run



on our engines, its a dual device - separately handles both Lp and HP pumps


VST vent should be simple to check/disconnect for testing


I am remembering now, that I once posed the question here,

but no responses:

why does Mikuni (maybe not on all - but typically) put TWO vents on the VST cover?

[boscoe99]

why does Mikuni (maybe not on all - but typically) put TWO vents on the VST cover?

Are you venting again about this?

That now makes TWO vents.

Two vents are better than one. Results in less vacuum build up.

[fairdeal]

Two vents are better than one. Results in less vacuum build up.

that word again!

[99yam40]

larger filter with a smaller micron media may be where they were trying to go with this.
Just make sure what ever you put in the system still allows the proper fuel flow once it is modified

[zenoahphobic]

larger filter with a smaller micron media may be where they were trying to go with this.
Just make sure what ever you put in the system still allows the proper fuel flow once it is modified

A proper designed as a "replacement" smaller micron filter must be larger to a size that has the same resistance to fuel flow. Simply, if you half the microns the resistance doubles, so the smaller micron filter must have atleast double the surface area that the fuel can evenly flow through, plus a reduction (thickness if you like) in distance that fuel needs to travel through the filter as the resistance within the filter also doubles, very simplistically.
And of course one would need a larger smaller micron filter as more material will be filtered and held within. More consideration to more frequent changes will be necessary.

[99yam40]

yep, and probably the reason Yamaha does not recommend going to a 2 micron

[pstephens46]

Googled micron. 1 millionth of a meter? Pretty damn small.

[boscoe99]

that word again!

Stated a different way in a different Yam document. But this document relates to an F9.9 built by the French. I suspect the document was written by the frogs for the japs.

[99yam40]

Googled micron. 1 millionth of a meter? Pretty damn small.

I believe Yamaha recommend a 10 micron filter

[panasonic]

What is "vacuum pressure"?

There is pressure. More pressure or less pressure. Less pressure all the way down to zero pressure. More pressure as far as infinity.

Boscoe does not like the use of the word "vaccum". Well, maybe in a vacuum cleaner it is OK but not for a motor. What some will call an engine.

Yamaha places their fuel pumps downstream from the fuel filter. Such that the pump has to do more work. Sometimes Yamaha has to use two or three mechanical fuel pumps to get the job done.

Mercury places the filter after the fuel pump. Generally only one fuel pump is needed to do the job.

Based on the way the fuel system is designed in a Yamaha there is a concern with respect to fuel starvation. Adding any additional fuel filtration causes the restriction to fuel flow to rise. I suspect that once upon a time Yamaha did not want a boat mounted filter installed. Once they realized the one on the motor was insufficient for the task at hand they started endorsing boat mounted filters. And then cautioned their mechanics to be sure there was still sufficient fuel flow to the motor.

Funny how different parts of the world call things. Where I am from a motor is electric. A outboard is an engine.

I hear "What kind of engine did you buy for your boat?"

or

"Did the starter motor burn up on your outboard engine"

I hardly ever hear "You got a new a new outboard?"

LOL

[zenoahphobic]

Are there any standalone pump/small tank/2micron filter systems out there that will offer this extra filtration between the fuel tank and engine, that would not add/change the load on the existing onboard engine fuel system?

One could make something I suppose. Would this increase or decrease reliability?
Would there be an issue with venting perhaps?

[boscoe99]

Are there any standalone pump/small tank/2micron filter systems out there that will offer this extra filtration between the fuel tank and engine, that would not add/change the load on the existing onboard engine fuel system?

One could make something I suppose. Would this increase or decrease reliability?
Would there be an issue with venting perhaps?

Yes. One is made by Racor. The filter people.

Has an integral pump so the primer ball can be eliminated.

A vacuum gauge can be added so as to monitor the level of fuel flow restriction as debris is captured. No more guessing as to when it is time to change a filter. Leave port knowing that the filter is in perfectly good condition.