Re: Dellorto carb questions

[bearbvd@domain.elided (Greg Hermann)]

I don't kow these carbs "personally". DO they have air bypass needles for
adjusting the amount of air going in at idle (as well as for balancing the
individual throats?? (Such as some of the later Weber DCOE's have.)

If so, it is entirely possible that these have been opened up far to much,
and the throttle butterflies themselves are therefore not positioned in the
correct relationship to the first progression hole as you come off idle.
This condition (butterflies too far closed with respect to the first
progression hole at idle) will _absolutely_ give you a lean stumble coming
off of idle. The butterflies should just begin to expose the first
progression hole _immediately_ as the throttle is moved off of idle. With
DCOE's, there is a brass inspection plug over the progression holes so that
one can inspect the position of the butterflies with respect to the holes
(using a strong light). I assume that your Dellorto carbys would have
something similar.

Get the relationship between the butterflies and the progression holes
right, and you may well discover that some (so-called!!) "expert tuner" has
richened up the idle circuit (well beyond where it should be) in an effort
to get rid of the lean stumble caused by the first error !

Greg

At 11:06 AM 12/13/01, David Rubie wrote:
>Some more experienced Alfisti might be able to help me with this.
>
>Long story short:  Trusty the Alfetta has a set of 45mm DHLA carbs
>in place of the factory 40mm items, replaced by the previous owner.
>He (fairly obviously) never really got them to work properly and neither
>have I satisfactorily, although I made a recent breakthrough which shed
>some light which I'll detail.
>
>I bought a Dellorto factory book some time ago but hadn't bothered
>opening it until recently.  I've been driving around for a couple of years
>with a massive flat spot off idle (which can be ameliorated with careful
>application of the throttle) but just how bad it is was demonstrated when
>a friend of mine drove the car (with me in it) and nearly stalled at every
>intersection.
>
>When re-fitting the carbs last time, I had forgotten to adjust the
>accelerator pumps.  In fact, they were totally loose and not
>contributing anything.  Once I had this (sort of) sorted out
>the big flat spot has *almost* gone, but I'm still left with a
>directly off-idle stumble that I think is now fixable.  I'm
>not discounting the possibility of vacuum leaks, as the
>carb rubbers are well overdue for replacement.
>
>Does anybody have any idea about the steps used to get
>the progression right from idle to accelerator pump
>actuation?  The Dellorto book and the Haynes manual
>give conflicting advice about where the idle screws should
>initially be set at (Haynes says 4 complete turns, Dellorto
>say 2.5).  I'm not 100% sure that the stumble is from either
>a too-rich mixture or too lean, although the occasional back-spit
>suggests too lean.  If anybody has been through this before, can
>you offer me a few tips?
>
>Thanks in advance,
>dave.
>1978 Alfetta GTV "trusty"
>1975 Alfa Spider Veloce "rusty"
>1994 Volvo 850 T5 wagon
>
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