What supplies the additional fuel when VBoost kicks in

[Falaholic]

Since the carb is getting additional fuel from the adjacent carb, how is it getting the additional fuel with the advent of the additional air?

 

[Fire-medic]

Carbs work on the venturi effect, air passing the fuel supply tubing creates a differential in the air pressure and since air/fuel mix wants to go from an area of higher concentration to one of lower concentration, the fuel is pulled from the other float bowl passage and into the VBoost, and then the inlet tract to the combustion chamber.

Ever see a time lapse of traffic in a crowded transit terminal? The flow speeds up, slows down, but keeps moving. During the intake phase, w/the intake valves open, that cyl gets the double charge, and when the valves close, the additional flow stops, as does the flow from the primary carb. Then to the next cycle.

Since the linked carbs only have one pair of inlet valves open at one time, the fuel/air mix flows towards the open inlet tract. Forward-back, repeat every other crankshaft revolution.

 

[Hellboy]

Nice explanation, Nothing to add.

Matt

 

[MaxMidnight]

Just in case it is needed a little elaboration on the venturi.

The venturi is the narrow part of the carburettor inlet tract.
As the piston descends with the inlet valve open it sucks in air. At the narrow point in the carb. it need to speed up to get through the restriction. This causes the air pressure within the venture to drop.
A jet connected to the float chamber exits into the venturi.
As the float chamber is at ambient pressure and the air flowing through the venturi is below ambient then fuel is drawn into the venturi.

That's all very well, I hear you say, but show me the maths's behind this.
OK, have a look here.
Happy? No? So you are more of a pictures type? No prob.
Have a butchers here.

The same principal helps aeroplanes fly, football swerve and to make the seemingly most un-aerodynamic piece of screwed up paper miss the bin even when you are standing over it!

 

[Fire-medic]

Just in case it is needed a little elaboration on the venturi.

The venturi is the narrow part of the carburettor inlet tract.
As the piston descends with the inlet valve open it sucks in air. At the narrow point in the carb. it need to speed up to get through the restriction. This causes the air pressure within the venture to drop.
A jet connected to the float chamber exits into the venturi.
As the float chamber is at ambient pressure and the air flowing through the venturi is below ambient then fuel is drawn into the venturi.

That's all very well, I hear you say, but show me the maths's behind this.
OK, have a look here.
Happy? No? So you are more of a pictures type? No prob.
Have a butchers here.

The same principal helps aeroplanes fly, football swerve and to make the seemingly most un-aerodynamic piece of screwed up paper miss the bin even when you are standing over it!

I can vouch for this, as it happens to me about 20% of the time. :confused2:

Good to hear from you, Mr. Midnight. Thank-you for the elucidation. Clear and concise, and accurate.

 

[Falaholic]

Next question.
Is the transfer tube right at the venturi?

 

[Traumahawk]

It should be the Vboost tubes right under the carbs.....where the Vboost butterflies are.