Filing SU needles


(Phil.Dobson) #1

what’s the consensus on the reported ability of some tuning people to be able to ‘file’ the mixture needles to improve performance on modified engines?


(Andrew Waugh) #2

My experience is that about 5% of the modified needles have been done by someone who appears to have an idea of what they’re doing.

The proper way to do it is to lay the needle on a wood block and drawfile a flat in the range where you want more fuel.

I’ve found bent needles, crimped needles, needles with hourglasses sanded into them, needles which have been rubbed on a brick… but only a few which have a clean flat obviously done to make WOT a bit less lean.

Of the poorly done needles I’ve found, most of them have been modified down about where the car idles… SUs have screws for adjusting idle mixture.


(tony) #3

If you wish to consider it, first acquire “How to power tune SU carbs” by Des Hammill

It has very detailed instructions on how to do it, and the reasoning