Weber rebuild

Ferrari Message Board Archive 10/00-8/02
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Weber rebuild

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Posted by Larry Skinner

I'm going to rebuild the 40DCNF carbs on my 78 308GTS.  I've rebuilt several Hollys but never a weber.  Anybody out there have any tips or gotchas I should be aware of?  Thanks!
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Re: Weber rebuild

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Posted by Kerry

There was a series of 3 articles in the Prancing Horse issues 78-80 (~1986) that covered rebuilding of Weber carburetors.  The carbs were a 6-pack (275 GTB?), but the concept should be the same.

If you email me your address, I can post a photo-copy to you.
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Re: Weber rebuild

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Posted by Deane

They're pretty straightforward, simpler than the Rochester spread-bore I used to try to keep alive.

The critical things to check are throttle shaft wear (creates an air leak at idle, wiggle the shaft when the throttles are closed, shoudn't move sideways much at all) and body straightness (flatness at base), otherwise it's disassemble the carb, dip, and put it back together.

That's probably also a good time to check all your jets and emulsion tubes against the factor recommended sizes to see if any or all of the jets have been altered, which is pretty common. And of course the condition and setting of the float and needle.

Angelo Wallace's shop manual translation is a pretty good resource for the basic carb operation and adjustments, and factory jet sizing.

Once your carbs are together but still on the bench, carefully check the synchonization of the throttle plates opening off idle.

Balancing the individual barrels' airflow on the car at idle requires a synchrometer but is pretty straightforward once you think about it for a bit. You do the work between carbs with the idle screws, then equalize the barrels within the carb by means of small idle air bleed screws on the side.

Setting the idle mixture is best done with an exhaust gas analyzer, but you can do OK by ear with experience. The pros use the gas analyzer.

Mike Pierce at Pierce Manifolds (408) 842-6667 in Gilroy, CA is the leading Weber parts supplier in the US as far as I know, and he does rebuilds and repairs for folks all over the US. I've seen pallets of new Webers at his shop, and perhaps a dozen long racks of individual carb parts by part number, including hard-to-get oversize throttle shafts.

Mike straightened out my badly warped carb bodies in an oven fixture over several days, and did a really nice job. Mildly warped bodies can be flycut (the usual shortcut), but mine were more than 1mm out of flat!

Mike is a high quality individual whose entire business is Weber carbs and installations, so if you need any parts or advice, he's the first guy I'd call.
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