Needle recommendation?

[Perseverant]

My XK120 runs pretty well, but I've always reckoned that it runs rich - dirty plugs etc. The engine is a mildly tuned 3.4 from an "S" Type of the mid sixties, with 2" SUs. When I first got the car some 10 years ago I discovered that the needles were the "richest" available and went down two sizes. I wonder if anyone out there has any suggestions. I think that the current needles are UM.

[mph]

Perhaps your best bet is to get it on a rolling road and find out exactly in which part of the range it's running rich. That will help you to select the best needle for the job.

There are a large variety of needle profiles available, and depending on what you go for, they will change the mixture to varying amounts at various points across the range.

Having said that, someone with more practical experience than I, can probably comment on the most likely options to try.

[Perseverant]

Thanks for the comment and suggestion. My own fiddling about improved fuel consumption quite a bit, not to mention oil use, though the best thing as far as that is concerned was to fit a spin off filter conversion as the old one leaked constantly. Been great fun in the recent hot weather!