Raise and hold. The rpms should momentarily rise then settle back down
again. If they rise and stay up the mixture is too rich, if they fall it is
too weak.
Air-flow balancing is a two-part process. The first is to get the idle
screws set, then when you have the mixtures balanced you retighten all
spindle clamp screws, then re-check the air-flow balance at about 1500 rpm
set with the throttle pedal. This ensures that balance is still mainytained
when driving, which is far more important than when idling! There should
also be a small clearance between the lever on the throttle spindle and the
choke spindle when the throttle is closed to ensure the idle speed is being
set by the idle screws and not by the throttle pedal stop.
You might like to cast your eye over the setup info on the site below -
select 'Spanners' and 'SU Carbs'.
PaulH
http://www.mgb-stuff.org.uk
----- Original Message -----
From: Phillips, Frank <fwp@ufl.edu>
To: <mgs@autox.team.net>
Sent: Tuesday, August 08, 2000 8:27 PM
Subject: SU update and question
> List,
>
> First, thanks for all the help. Things are looking better!!! I have
centered
> the rear carb now and it rises and falls perfectly. Now I'm trying to tune
> my SU HS4's for the first time.
>
> Here is my question: Once the air flow is balanced at the stated RPM and
the
> mixture is played with to give the best running condition the instructions
> say to raise a piston 1/32" to check the mixture and see what happens to
> RPM. Do you raise it and hold it, or raise it and release it?
>
> Thanks again...
>
> Frank
> fwp@ufl.edu
> 1968 MGB http://plaza.ufl.edu/fwp/mgb.htm
>
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