[T3] Carbs Questions

["Mark Seaton" <mark.seaton2@ntlworld.com>]

<x-charset iso-8859-1>Well I've just got done stripping a couple of pairs of carbs I recently
scored on ebay and have a few questions for the list (sorry I know most of
you are FI'd, and I sometimes wish I was too but FI's a rare thing over here
in the UK)
Ones a late pair (PDSIT 32/34s) and the other an early pair of PDSIT32s (not
a matching pair as one seems really early with VW stamps on all the parts,
and a side entry for the main jet).
I need to build a decent pair out of the 4, but noticed a few strange
differences.
The early pair have a piston device instead of a rubber diaphragm to release
the throttle advance in the choke mechy. I prefer the idea of this so am
thinking of using the early top parts. The bushes for the shaft in the choke
mechy that advances the throttle seem better designed on the early ones as
there is much less slack- which should mean more even throttle lift and
smoother cold running.
The castings of the earler ones are generally much better quality and
finish- they are not nearly as coroded as the late pair, and the steel parts
have a nicer looking plating (cadmium?).

The early pair have different sized jets left and right. I thought this must
be a mistake but when I looked in my Haynes, sure enough up til '71 this was
as spec'd. The left carb has larger main and air correction jets- I guess to
ensure the left bank runs richer and cooler than the right to make up for
the poorer cooling on the left. This changed in '72 to equal sizes both
sides. My first question then is should I stick with the specs for my engine
(a '73), or go with the earlier design which seems to make good sense?

The throttle plates are also subtly different.
The early pair have a brass idle screw with a spring and a much blunter
point. This screws into a larger jet in the wall of the plate. There are 3
small holes (jets) in total- 2 below the adjustable one. The throttle disk
is plain on its underside.

The late pair have steel plated screws without a spring but with an o-ring.
The points are finer and engage in a smaller jet in the plate wall. There
are 4 jets in total, but they are all a lot smaller than the earlier
version. The throttle disk has cutouts on its underside over these jets, and
on the left carb, over the hole for the dist vac take-off. The late idle
screw has a much finer pitched thread than the earlier version, so I'm
wondering if this could explain why I need to turn the screw out about 3
turns for smooth running when all the manuals say it should be about 1.5
turns -the Haynes only has pics of the earlier style carbs.

My third and final question concerns re-bushing the throttle plates. I
dismantled them all and to my suprise they all appeared to have been
re-bushed allready- and in exactly the same way. They all have counter-bored
journals with PTFE linings (loose) with brass ring capping pieces. So the
question is- was this how they came from the factory, or have they all been
overhauled in the past. Seems too similar to be the latter, but I suppose it
could have been a VW approved method. Anyway, the PTFE being very soft, has
gathered dirt in all of them, and acted like sandpaper and really grooved
the shafts. I plan to counterbore them further to 10mm dia and press in
Glacier bearings. These are metal backed with PTFE/lead composite linings
which I think can be reamed after insertion. I'll just have to smoothen the
burrs on the shafts and hope its better than nothing.

Thanks for your time,
Mark Seaton
'73 TA

PS: I browsed into this neat site this morning . They make these interesting
horizontally opposed engines based on the "scotch yoke" where the two
opposing pistons are fixed to a rigid common conrod, with a vertically
sliding bearing to follow the circular motion of the crank. Supposed to be a
lot smoother running, longer lasting etc. Would be neat if they made an
aircooled one ;-)
www.cmcpower.com


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