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?
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.
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