[Spridgets] SU carb basics help..

[Lester]

Hi all,

so over the last month I've been trying to get my 1380 engine to idle at
something less than 3000 revs to no avail.  I've looked at the needle and
found it to be a "1" but at idle step, all the jets are the same so after some
more messing around I found that the rear carb piston is moving higher than
the front and won't go any lower, so to match flow I have to increase front
carb idle setting (NOT mixture).

I spent a fair amount of time re-working Jag SU's and one of the critical
things about them is that the butterfly, when closed, is centered and fits
tightly.  This is checked by holding the butterfly closed and putting the carb
up to a light to see how much if any light comes into the barrel.  So I tried
this with the AUC's and find that there is light all around the butterfly
which means that even when it's closed it's not REALLY closed.

What I don't know is if this is as important with the AUC's as with the Jag
carbs (HS 8 or HD 8).  Is it common racing practice to install smaller
diameter butterfly?  Are they all like this?  Is there something I'm
missing??

Thanks all,