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[T3] Effect of fuel pump pressure


A few weeks ago Bob Heydt sent me a spare carb from a dual carb type 3. I had 
asked to borrow one so I could take some measurements to determine what the 
effect of having the "wrong" fuel pressure might be. Last night I finally got 
around to looking at it. Here's what I found.

The carb was a late one, a 32 PDSIT-3, 341-129-026B.

After working thru everything, and correcting all my mistakes, it looks like 
the gas level in the float bowl will rise somewhat less than .015" for every 1 
psi that the pressure rises. This is for the 1.2mm float valve.

If you have an earlier carb with the 1.5mm float valve then the level will rise 
about .020" for each 1 psi increase in fuel pressure.

This turns out to be more of a change than I expected, but it's still not much. 
I think this amounts to much less than a 5% change, so it's a lot less than 
changing one jet size.

I should also point out that, because the float is tapered, the real numbers 
will be somewhat LESS than the figures above. I just didn't know how to do the 
calculation exactly, so I had to make some simplifications.

Thanks to Bob for loaning me the carb. It's packed up now and I'll get it back 
to you some time this week.

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

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