About the two sets of needles you have.
Assuming that the engine you will be contemplating their use on as a 1275
dual carb model some info is below.
There are 16 or 12 steps on each needle with the following diameters:
STEPS AAC M
1 .089 .089
2 .0855 .0855
3 .0835 .0832
4 .0811 .0808
5 .0788 .0785
6 .0765 .0763
7 .0742 .0745
8 .072 .0726
9 .0698 .0707
10 .0676 .0688
11 .0655 .0669
12 .0631 .065
13 .061
14 .059
15 .057
16 .055
Up to step 6, the M provides more fuel due to its smaller diameters.
Beyond that it would run leaner.
The AAC is listed for the 73-74 Mark III Midget as the standard needle
with the use of blue springs. There are no weak or rich needles listed
for those years
The M is listed as the rich needle for the 1969 MG1300 or the 1971 MG1300
Mk II, or their corresponding Austin marks, again with blue springs. Blue
springs are what are used in nearly all Spridgets. It also is listed for
some engines other than 1275 dual carb jobs, but I don't think that info
is of any particular use.
Paul
PAsgeirsson@juno.com
On Thu, 10 Dec 1998 10:19:27 +1100 Eriks Skinkis <eriks@netspace.net.au>
writes:
>I have two sets of 1.25" SU carb's. Looking at the needles one pair
>has
>the later type spring loaded needles stamped "AAC" while the other
>pair
>has the earlier type fixed needles stamped "M".
>
>Is there much difference between the "AAC" and the "M" needles, would
>one be better than the other?
>
>Thanks,
>Eriks.
>
>Midget '70
>
>
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