The 'E' Type Forum

I'm trying to tune the SU's on my 4.2. It's an American import, changed to SU's by a previous owner. The carbs look as if they've been rebuilt, but the needles have been seriously ground down along most of their length - tapering out to normal at each end. I seem to recall the tuning brigade doing this sort of thing, but it seems a bit radical to me. Should I junk them and start again with new needles? If so which ones should I start with?

According to its number, my engine is a low compression unit (8:1). But this may of course have been altered along the way. I've done a compression test and get readings of between 163 and 170 for 5 cylinders, with one down to 150.

Any advice greatly appreciated.

If your car is running in a standard set-up (drum air filter, unmodified engine) then go with a new set of standard needles - UM. They are cheap and do wear with use so start from a good known benchmark as I doubt you will need anything else. Here are some guides from our Knowledge Base to get you started:

SU Carburettor Notes: http://www.jcna.com/library/tech/tech0006.html
SU Search (SU needle comparison spreadsheet): http://homepage.mac.com/crscapps/CSA/Page1/Page1.html
WinSU: SU tuning software: http://www.winsu.co.uk/

Thanks David - I acquired some standard needles as you suggested and they've made a great improvement.

I'm now in the same situation. I've got hold of a set of HD8s on a manifold for my dad's US spec Series 1.5. However, one needle was missing. I'm contemplating fitting a PiperX filter. In theory this will mean a different needle, but would it also in practice? As this car has got a lower CR than a UK spec one, would this mean a different needle? UM for me as well?

Be careful about what filter you use - check out this thread: http://etypeuk.com/forum/viewtopic.php?t=3394 If you use anything other than the standard drum filter you will need to change the needles for something richer. Also worth remembering the needles do wear so fitting a new set can produce some nice results

David : if I may make a small correction, these fixed jet type needles should not wear at all provided the jets are properly centred . It was when SU went to the spring loaded swing type needles that wear became an inevitability because then the needle was designed to be in contact with the side of the jet