TECHNICAL INFO  

 SU CARBS 

SU Carbs - Quick reference needle selection 

Unfortunately I cannot give an all-encompassing table of what needles are needed for which engine builds. My life's collection of all the automotive-orientated work I'd ever done was stolen out of my car by some low-life scum a few years back. Not for what it was - but for what it might be. All I have is a few scribbled notes, the source of where I start now. Being an oft-voiced question on the message board, I thought I'd share it with you. Since there is already a very good source of starting points/applications for fixed needle carbs, this is for those floundering about in the wilderness that is the biased (swinging) needle example of the breed. 
 
These are based generally on 1275cc+ motors, using a reasonably modified head, compression ratio on the sane side for unleaded road use, and uses Kent Cam profiles as the main guide so just select one that near-matches what you're using 
 
Std filter case K&N Cone or 
With K&N filter Pancake filter 
Single 1.5" 
MD256 AAK AAU 
MD266/7 AAA AAM 
MD286 AAM ABY 
 
Single 1.75" 
MD256 BDL or BAK BDK 
MD266 BDK BCE 
MD276/286 BBC BBC 
MD296 Modified BBC…………… 
 
Twin 1.5" (assuming K&N pancakes or no filters) 
MD256/266 AAV 
MD276 AAA 
MD286/296 AAM or ABY (ABY is richer towards top end). 
 
Other references - 
These are for comparison and are arranged going from leanest to richest. Makes a good visual example of what happens where on the needle profile in accordance with engine specification when the profile list of each is lined up in a row. 
BEJ - standard unleaded Metro. 
BER - 1.3 Pre-injected Cooper (basically MG Metro spec engine). 
BFA - Alternative Metro Turbo needle, has richer cruise section, but leaner top end. 
BDD - Metro Turbo standard needle. 
BFY - 1.3 Pre-injected Cooper unleaded (basically MG Metro spec engine). 
BDL - MG Metro standard needle. 
BCE - Popular modded engine needle (see above table). 
BBW - 1.3 Pre-injected Cooper with Stage One kit using K&N cone/pancake filter. 
BDK - 1380 fast road spec (MD286, modded head, etc.). 
 
NOTE: 
When choosing a different needle, select one with the same idle figures. If this is not possible, remember - 
If new needle has a leaner idle figure, the rest of the needle will give a slightly RICHER mixture than the profile suggests. 
If new needle has a richer idle figure, the rest of the needle will give a slightly LEANER mixture than the profile suggests. 
This is caused by re-positioning of the jet to get correct idle mixture. 
 
Like I said - these are merely starting points - so a healthy dollop of sensibility is needed! I highly recommend buying the SU needle chart book available - part number ALT9601. Not only does it list all the needles and their profiles, nut a useful section in the front giving suggestions on how to select a different needle than the one you're using.