Carb info please

[dalgrae]

I have an AUD13 fitted to my 948cc engine but have always thought it was running a bit rich so I decides to take it apart with the following results.The needle is marked AN and not as should be M I have read Roys posts from 2009 relating to a similar carb problem and tried his method of checking the fuel height from the jet hole 1/4 below this but I cannot see a way of doing this as the hole is small in diameter so Roy please explain again to me ,also do I have to centre the jet as per the workshop manual as I cannot understand what can move to achieve this,I have read that the basic setting for the mixture control nut is approx 2 and a half turns out but I am already below 2 turns and as Roys previous posts say the M needle is actually richer.

[bmcecosse]

You just have to look down from above and make a judgement. Pull the choke down - it may be more obvious then, The 2 flats etc is only a very rough 'starting point' - don't put too much faith in it... The jet may well be worn - it may have been in there for 50+ years!

[philthehill]

You have the right needle AN for the carb AUD13 - 1 1/4" HS2 and which is normally fitted to the 1098cc Minor. The weak needle for this carb is EB.
The M needle is fitted to the H2 carb. A BX1 needle may be fitted to the H2 dependent upon serial number of the carb. Full details on the Burlen web site.
For overhaul and adjustment details see http://sucarb.co.uk/technical
Click on H2/HS2 details on the left of the page.

[mike.perry]

The mixture nut should be turned fully up then 2 complete turns or 12 flats down as an approx. starting point then fine adjusted from there. The M needle is listed as the standard needle for the H2 and HS2 carbs.
To compare needles go to http://www.mintylamb.co.uk/suneedle

[philthehill]

mike
The AN needle is the correct needle for the AUD13 carb which was only fitted to the 1098cc engine.
You are right in that the M needle was fitted to HS2 carb AUC944 1960 - 1962.
The M needle is not the correct needle for all H2 carbs fitted to 948cc Minors though.

[bmcecosse]

Perhaps the needle changes were to reflect changes in the air filter...or maybe to try to ease out a little more economy to look better in Road Test comparisons? There were no engine spec changes to justify different needles...The changes are in any case almost insignificant. The mixture is more likely now to be influenced by wear in the jet and/or needle - and float level.

[dalgrae]

Thanks for all the advice but I still cannot see what/how the jet centering works looking at all the individual parts and when assembled there is no leeway for any adjustment at all

[dalgrae]

OK have reread the SU instructions again and I think I now understand how to centre the jet I have ordered all the new parts to overhaul the carb so will see what happens when they have been fitted

[bmcecosse]

The later HS2 (not a railway..) carb has no need of jet centering - and has the much better port on the side to suck away the nasty fumes from the rocker cover much more efficiently - without plastering the paper filter with gunge.