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Re: [T3] Update on fuel pump adjustment

On 21 Jan 2003 at 16:00, Steven Ayres wrote:

> For the T engines -- Type 3, 1600 dual carbs -- flow rate was also set at
> 400cc, but the max pressure spec goes up to 5psi +40%). The footnote to max
> pressure may provide a clue as to why:

I think someone mentioned this before, and also pointed out that VW also 
changed the RPM where the spec was met. Since the delivery will go up with RPM, 
this looks to me like it is perhaps no change at all.

> "Via 1.5mm (.059in.) diameter float needle valve (1.2mm (.047in.) diameter
> on Type 3 / twin carburetor)"

This MAY be the whole difference. The whole pressure thing is dependent on the 
area of the float needle valve that is exposed to the pressurized gas. Since 
the float valve is a circle and its area is proportional to its diameter 
squared, to make everything work out the same in the end you would need greater 
pressure in proportion to  (1.5mm/1.2mm)squared. This works out to 5.5 psi, 
which isn't half bad.

Still, I have no idea why they thought it would be a good idea to change the 
float valve sizes. Keeping them the same would have been a much simpler 

I'll know more when I get my hands on a carb. Is there one in the mail??? (I'll 
gladly return it when I'm done.)

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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