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BF225 VST operation

James t

Member
New to this forum and my 2004 BF225 so sorry if this is a bit of a basic question...

I can’t find anywhere that explains in detail how the VST works. I think I understand the basics: low pressure/lift pump feed to VST with float switch feedback, High pressure feed to fuel rail, pressure regulator feedback. But what else is going on and where does the vapour part come into it. Are there other fuel feedback routes into the VST from the fuel rail? I was looking for a diagram with a step by step explanation if anyone has something like that.

i want to do my own servicing and so want to understand this as best I can.
 
The VST is in place to assure an adequate amount of non-turbulent fuel is available to the high pressure fuel pump. The fuel in the VST tank is kept under pressure to prevent vaporization, thus preventing the fuel from becoming too lean under variable demand.
 
That makes sense thanks. Am I correct in thinking the high pressure regulator ensures a constant fuel rail fuel pressure regardless of demand from injectors and if pressure spikes the regulator provides a feed off the rail back into the VST?

i assume spikes occur due to sudden drops in revs? And that the VST design aims to ensure consistent pressure at the rail for fuel efficiency purposes?
 
Hi.
I have the shop manual for a Bf130.
I “believe” that the 225 is very much similar.
The fuel is drawn through a diaphragm pump which runs off one of the camshafts.
The diaphragm pump chamber has spring loaded check valves.
The fuel then goes into the VST through the needle float (which in turn closes the incoming fuel supply once the VST container is full to prevent overfilling).
From there the fuel is pressurized by the electric pump and through a high pressure filter which is always running regardless of the fuel demand.
Once the ignition key is turned on the the high pressure pump will run for 2-3 seconds to pressurize the rail.
Once the engine is on, the electric pump feeds pressurized fuel to the rail where injectors dispense it into the cylinders.
THE REMAINING fuel is allowed to flow back into the VST container through a hose and is available to go back around.
The fuel regulating valve on top of the injector rail Which is connected to the air manifold increases / decreases the amount of escaping fuel with a needle valve and a diaphragm therefore keeping the pressure steady regardless of rpm and or load.
The VST container has a hose through which gasses and air are allowed to vent out (once it’s through a strainer) into the leg of the outboard.
All the above refers to the VST of the bf130.
I have just bought a brand new Bf250 drive by wire.
I very much think the whole fuel supply plumbing is the same or similar.
You could google bf225 shop manual and you can find a pdf 535 pages which illustrates all this.
chawk_man and some other guys are pros, I am not.
hope this helps.

 
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