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Re: New topic follow up from CR discussion...

To: 6-Pack <6pack@autox.team.net>
Subject: Re: New topic follow up from CR discussion...
From: Don Malling <dmallin@attglobal.net>
Date: Tue, 23 Dec 2003 23:40:05 -0500
Wow... forgot spell check...

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 acceleration, and the engine speed is not 
changing then the air valve is not rising. It stays at a fixed position. 
It that case (Constant 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.




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