Purpose of VST

[pstephens46]

What is the purpose of VST? Emission control? Seems like there are many issues around it. Hard to get to as well on F150.

[boscoe99]

Its purpose is to remove vapors (air bubbles if you will) from the fuel supply so that the fuel pump sees nothing but air bubble free gasoline.

The inlet of the fuel pump is at the bottom of the VST. Air bubbles in the gasoline rise to the top and are eliminated.

You would not want a mixture of air and gasoline to be sent to the intake system via the fuel injectors. The motor would not run well at all.

I agree that the VST, pump, filters and such can be a pain in the ass. Wouldn't it be nice if the fuel pump (one and only one) was in the bottom of the tank in the boat? Mostly trouble free just like most automobiles and trucks are.

[TownsendsFJR1300]

Besides the above, like your car, you have an electric fuel pump in the gas tank (to keep the pump cool and full access to fuel).

Being there's no fuel tank on the engine, the VST is like a carburetor with the HP fuel pump inside (it literally works like the gas tank in your car-but just for the pump keeping it cooler and fuel to it all the time).

Just as a side note, I'll drain mine (drain screw) and flush(primer bulb) every once in awhile to keep it clear of debris..


+ 1 on PIA access to the F150's.

I've never pulled my filter. It was checked once while under warranty (for the dreaded low idle issue)

[pstephens46]

Thanks for the info. Haven't touched mine. Hoping that non ethanol fuel may prevent issues.

[fairdeal]

Being there's no fuel tank on the engine, the VST is like a carburetor with the HP fuel pump inside (it literally works like the gas tank in your car-but just for the pump keeping it cooler and fuel to it all the time).

Personally, I like to think the VST is EXACTLY "a (miniature) fuel tank on the engine"

[rodbolt17]

unlike yor ferds chebbys and dogdees, when that motor left Yamaha Japan ,Yamaha had no idea wjo's hull or what hull it was going on.

\therefore the engine has a mini gas tank so the hp pump can get a vapor/bubble free fuel supply.

I can do the VST about as fast or slightly faster than most techs can do a set of carbs on a 2 stroke 150.
way faster than any tech can do a set of inline 3 or 4 carbed four stroke.

if you spend much more than 2 hours cleaning the F150 VST and servicing the injectors,you're milking it.

occasionally if its really bad due to water 3 hours.

[cpostis]

SX150TXRZ-Fuel Injected

OK, now that the VST is brought up, I have a question. I was thinking of adding a fuel management sensor/gauge to my boat. I've read that with a VST, it would not be compatible due to the float and valve and the fuel return line. I don't understand this. The fuel sensor will be mounted directly after my fuel water seperator/filter and before my on engine fuel filter.
Maybe I won't get an instant reading, however all I want to do is monitor my fuel usage over a trip.

Do you guys see any reason why I cannot perform my goal in this situation.

[rodbolt17]

depending on flow sensor sensitivity, it will read flow at all speeds set up that way.
dunno where you read something silly like the VST messing with the flow sensor but ya might stay away from there.

[cpostis]

OK, my mistake. I just reviewed the info. The info reads: "Does not work with diesel engines or any fuel system with a return fuel line or sump".

I'm assuming they mean return line to main fuel tank (not my situation). The sump part, I don't understand.

I'm going to order the sender and give it a shot.

Thanks Rodbolt!

[TownsendsFJR1300]

I can do the VST about as fast or slightly faster than most techs can do a set of carbs on a 2 stroke 150.

if you spend much more than 2 hours cleaning the F150 VST and servicing the injectors,you're milking it.

I'd really like to watch you (or someone else VERY experienced), service one or two to learn... Once its accessed, should be similar to a carb but all the intake crap, and stuff its buried underneath, ahhh... I believe the biggest thing to replace is the HP pump filter...

With the past low idle issues (and now its fixed), I'm really shy about messing with it and inducing the issue again. A carb, or syncing them, I wouldn't hesitate to clean them/ sync with a 4 port vacuum gauge (Carbmate).

Agreed, a multi carbed engine will take considerably more time than one VST(basically one carb)...

[boscoe99]

OK, my mistake. I just reviewed the info. The info reads: "Does not work with diesel engines or any fuel system with a return fuel line or sump".

I'm assuming they mean return line to main fuel tank (not my situation). The sump part, I don't understand.

I'm going to order the sender and give it a shot.

Thanks Rodbolt!

Some EFI motors send part of their fuel supply either back to the fuel tank itself or to a sump. Or maybe a header tank. These systems may pump a large amount of fuel to the fuel injector rails (say 40 gallons an hour) but a large amount of that fuel then flows back to the main fuel tank, to a header tank or to a sump. The sensor is counting, measuring and displaying total fuel flow. So it won't work with these types of systems.

In a Yamaha motor all of the fuel that flows to the motor gets used by the motor. Even though some of it gets looped around to the VST, maybe through a fuel cooler. But the sensor is counting total fuel flow.

Now some Yams use an electric lift pump that operates intermittently when the engine RPM is below 1200. These will cause the fuel flow to surge when the pump runs and then the fuel flow plummets to nothing when the pump stops. The measured fuel flow is correct but the rising and falling fuel flow instantaneous values drive some folks wacko. Floscan cautions about using their fuel flow meter with this type of system.

I suspect that you are talking about a Lowrance sensor. They have no idea who all might use their system and on what sorts of fuel delivery systems. Of which there are many. And many. And many.

[cpostis]

OK, so as I understand it my SX50TXRZ OX66 fuel is drawn from the fuel tank to the boat fuel separator/filter (my boat fuel route), than through the on engine fuel filter via the low pressure pumps, sent to the VST through a float valve, picked up by the electric pump within the VST pressurizing the fuel rail, then through the injectors to the intake. Any excess fuel pressure is relieved back to the VST con*****ed by the pressure regulator through the return line. So in this case, no fuel would be recirculated through the fuel sensor if the sensor is located between the boat filter and the engine filter (or anywhere before the VST) thus ensuring accurate measurement by fuel flow sensor (within limits of said sensor).


Simple, got it!

Thanks Boscoe!