Re: 1750 carbs

[Simon Favre <simon@xxxxxxxxxx>]

The venturis on my 1750 are 32mm. I actually passed smog with those Webers
before it became smog exempt. Does the 34mm give more top end?  The most
important thing about rebuilding Webers is to be methodical, take your
time, and keep the parts in order. Use muffin tins, film cans, jelly jars,
anything to keep associated groups of parts together.

Gas leaking out after shutdown might be caused by too much fuel pressure
(3-5 psi is all it needs). It might also be a bad needle valve. This part
should be in the rebuild kit. 

Other things to watch out for:  Make sure gas sloshes freely in the 2
passages that pass under the float chamber.  If these are plugged, they
can be a pain to clear (drill bits and lead plugs). Make sure the bottom
cover fits tightly. If the threads in the body are sticking out, gently
file them down. The bottom cover can leak like a SOB.

I make sure the butterflies close by taking out the venturis and holding
the carb body up to a strong light.  Align the butterflies for the least
amount of light coming through with the idle screw out.  Make sure the
butterflies uncover the progression holes at the same time.  Be very
careful with the butterfly screws. They are brass. Don't get too carried
away trying to clean the butterflies. The holes and passages are more
important. If you can't get the butterflies to align, your shafts may be
twisted.

With the carbs back on the car, I set the F/R balance between carbs by
looking through the progression holes.  Crank the idle speed screw in
until the butterflies cover half of the middle progession hole.  Adjust
the balance screw until both carbs match.  Crank the idle screw back out
to a normal position.  The later DCOEs can't do this, as the progression
holes are permanently covered.  Mine have brass plugs that screw in.

Check the butterfly shafts. Open them all the way and rattle them. Some
end play may be acceptable, but there should not be any side play. There
is supposed to be a leather seal at the end. A sloppy shaft will suck
air. If the motor runs too lean as a result, you might burn a valve or
hole a piston.

I also polished the idle mixture screws by chucking them in a drill press
and squeezing the tips with a piece of Crocus cloth.

Good luck.

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