Before thinking I have weak needles, I did check fuel pressure, cleaned carbs, verified correct jets, needles and springs in the carbs, checked compression and valve timing and valve clearances. I also tried a couple of used coils.
I think this leaves me with needing richer needles, beginning around half throttle.
From the book Tuning SU Carbs by G.R.Wade, I see that I have all carb parts correct for '73 '74 4.2 XJ’s. The needle is BCC or CUD1150.
Has anyone a suggestion for another needle? This book has lots of info but no direction by part number.
I see a earlier year car uses CUD1133 or BBK needle.
Perhaps one of our Euro members will be more familiar with this.
This may be an ign timing issue rather than a mixture problem, Robert - depending on how 'lean mixture was diagnosed. It’s worth while investigating settings and dist advance mechanisms?
maybe your advance mechanism got lost during this year? - It all sounds as if advance wasn’t working properly. In standard setup the two HS8 with BCC needles are just fine; you can use red and green springs (both indicated even in my SII OM).
It looks OK, Robert - but any difference with and without vacuum connected?
It’s just, like others, I’m a bit apprehensive about the different needles’ influence. What about float levels - and indeed whether mixture, CO, has actually been checked?
