Mission for fairdeal; should he choose to accept

[boscoe99]

Your F225 I believe does not have a drain hose for the VST correct? How did you drain and measure the amount of gasoline that it holds?

In the other post currently being discussed about an F225 problem there seems to be some doubt as to whether or not the VST is being kept filled by the lift pump. What say you about screwing a hose nipple to the drain port on the VST, to which is attached a clear plastic hose. The hose will be routed upward to above the top of the VST and held in place with tape. When the VST is filled with gasoline the level of the gasoline within the VST will be seen in the clear plastic tube. A fluid seeking its own level being the theory.

As the motor is operated, and as the lift pump does its job (or does not do its job), the amount of gasoline being held within the VST can be monitored to see if all is in order. If insufficient gasoline is being provided then that would indicate a fuel supply issue to the VST.

[99yam40]

I believe you would have to take the shrader valve out for the VST to be exposed to atmospheric pressure for it to seek /indicate liquid level would it not?

Bosco see if you can reply to the F60 vapor lock thread. I do not sure where he should measure rail pressure on that thing

[boscoe99]

I believe you would have to take the shrader valve out for the VST to be exposed to atmospheric pressure for it to seek /indicate liquid level would it not? Good point. Possibly so.

Bosco see if you can reply to the F60 vapor lock thread. I do not sure where he should measure rail pressure on that thing

Way ahead of you on this one.

[99yam40]

Does that VST have pressure in it when running?
If so it would push fuel out no matter how high you run the open hose.
Maybe the shrader valve is just to vent while draining, but i would think yamaha put that valve in there for a reason.

Like keep it from venting to atmosphere all the time or hold some pressure to keep it from boiling as quickly maybe

[boscoe99]

The VST is vented to the air intake system. Fuel level rises with the float valve open and air is expelled to the vent system to allow fuel in. Fuel level lowers as fuel is consumed and air is admitted so the fuel level can lower. Fuel level lowers enough and the float valve opens so that fuel can come in and refill the VST.

Fairdeal can do the research and tell us for sure. I expect him to have this done by lunch time.

[99yam40]

OK so the VST is not pressurized while running I guess.
but why would the shrader valve be needed for draining if the VST is vented to the intake unless there is a check valve or some other way of closing off the vent?

[fairdeal]

The VST is vented to the air intake system. Fuel level rises with the float valve open and air is expelled to the vent system to allow fuel in. Fuel level lowers as fuel is consumed and air is admitted so the fuel level can lower. Fuel level lowers enough and the float valve opens so that fuel can come in and refill the VST.

Fairdeal can do the research and tell us for sure. I expect him to have this done by lunch time.

Darn.
Sorry to disappoint, but I am 1350 miles "away from home" and the F225.
I am up for the task, but it will have to wait a few weeks.

A hurdle for me may be the threads on that drain screw; not confident I have that die to make a threaded "hose nipple".

My immediate "intuition" is that the "top" of the hose will get Tee'd into the VST vent tubing, so as to neutralize any pressure in the headspace of the VST.

(As Boscoe knows) between the VST vent and the airbox is - depending on the model year - either a check valve or a non-moving restrictive orifice; in addition 2005 and later also has a check valve leading to the carbon canister.

The Schrader is there for venting - at least the SM tells us so.

[rodbolt17]

the sole function of the VST Schrader valve is to vent it when draining.

an easy way to tell if the lift pump is maintaining the VST fuel level is simple.
if it runs out of fuel it is not being kept full.

all the VST does is provide a small fuel tank for the HP pump to pickup a bubble/vapor free supply of fuel to pressurize the fuel rail.

the ONLY reason automobiles do not use it is because the auto was completely assembled when it left the factory.

the auto version of the VST is called the gas tank.

Master Craft and a few other inboards now run the pump in the fuel tank.

outboards have to turn left and right and up and down.

place a 45PSI fuel line in that extreme motion and I will guarantee it will fail and spray fuel at 45PSI everywhere.

the VST is not a magic box.

it is simply a small gas tank that is refiiled(make up fuel) by a mechanical or electric lift pump.
yes Virginia it is that simple.

[TownsendsFJR1300]

There's no drain nipple (for a hose) on the 225?

My 150 has the nipple and screw (along with a clear, plastic factory drain hose)
that would work easily as suggested W/O any mods..

Just secure the hose upward and loosen the screw...

[rodbolt17]

some engines had a drain hose, some did not.
some VST drains are so clogged with debris they wont drain anyway.

[TownsendsFJR1300]

some engines had a drain hose, some did not.
some VST drains are so clogged with debris they wont drain anyway.

They do have the nipple and screw thou, correct??

[rodbolt17]

dunno on every model. the old F115 did not.

if it has a nipple the hose is missing.

if it does not have a nipple it never had a hose.

this stuff is fairly simple.

[boscoe99]

They do have the nipple and screw thou, correct??

No nipple. Just a drain screw.

A Yamaha is not a Yamaha is not a Yamaha.

[pstephens46]

Would it be fair to conclude that the majority of VST crud issues are caused by ethanol? Assuming boat has water separator and engine filter?

[rodbolt17]

no it would not.
water in any fuel screws up the filters.

as the pump is a blow through design eventually brush dust from the pump motor will clog it.

water will also cause the tank to corrode inside and clog things.
water also causes the steel pump to rust.