Hi Shawn,
I think some of it is incorrect...
The amount of fuel that enters from the needle/jet opening is a function
of the difference in air pressure between inside the carb throat and the
external air. It's not a function of how big the needle/jet opening is.
The CD stands for Constant Depression or Constant air pressure or
constant vacuum. Kinda all the same thing.
As the engine turns faster it sucks more air and the air piston rises to
let more air into the carb. Since the air valve is rising there is more
air volume coming in so the depression/vacuum does not increase. Since
there is more air coming in there must also be more fuel to maintain the
same air/fuel mix ratio. Thus the needle must taper to expose a larger
"hole" on the jet to allow more fuel to enter.
The mixture (air/fuel) ratio should always be constant. No matter what
the engine speed is. The faster the engine goes the more air it sucks
and the more fuel it needs to keep the same air/fuel ratio. The air
piston rises and falls per the amount of air being sucked into the
engine so the air pressure passing over the jets always remains the
same. Thus the "Constant Depression"
In the case of acceleration you want the air/fuel mix to be richer, so
the damper oil slows the rise of the air piston thus altering the
"Constant Depression" There is more depression because the air is being
sucked over the jets faster than it normally would be. The air valve is
not as high as it should be so the air must pass over the jets faster --
more depression -- more vacuum -- more fuel gets sucked up through the
jet, for the volume of air passing over the jet and the mixture is
enrichened (is that a word?).
So if the mixture is lean during acceleration you would want the air
valve (piston) to move up slower not faster.
If we're not talking about acceleretaion, and the engine speed is not
changing then the air valve is not rising. It stays at a fixed position.
It that case (Contstant Depression) then the taper of the needle does
control the air/fuel mix.
The intro in the Haynes ZS manual explains this better than I did.
Don't know about the rest.
Don Malling
Shawn J. Loseke wrote:
> Thanks for all the input so far.
>
> I already have very thin oil in the dashpots.
>
> Please correct me if I'm wrong here. But as I see it is; as the needle is
> drawn up through
> the jet it tapers. If the mixture was lean I would want the air valves to rise
> faster to supply
> more fuel to the mix. If it tapers too quickly you get too much fuel.
>
> The B1AF is designed for 2 carbs on six cylinders and I believe has a fairly
> quick taper
> as each carb had to supply three hungry cylinders. With three carbs each carb
> is doing 2/
> 3's of the work it was meant for. If there is a needle with a more linear
> taper it should
> smooth out the mixture.
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