Needles for 2" SU carbs

peter weir

25 March 2015 at 21:59 #51196

I’m rebuilding an LG6 engine with Higher compression pistons, 6 branch exhaust and 2″ SU carbs.
Can anyone who has installed these carbs recommend the best needles for fast road/mild competition use.
Thanks for any feedback
Peter

David

30 March 2015 at 19:51 #51197

Peter, do you have access to the SU catalogue? If not I may be able to help. Which type of 2″ are you fitting?

peter weir

31 March 2015 at 22:27 #51198

Hi David
They’re off a post war Daimler 4.5ltr, not sure which but they’re HD8’s with manual chokes so they look pre-war.
I’ve got the SU book but a different types were fitted, with different needles and jets.
Whilst the engine size is the same, I wonder if the Daimler might be higher reving !!! Than the 4000 rpm LG6.
If we can get it running reasonably well, we’ll get it on a test rig to optimise the settings, but any help would be welcome to get a first set up.
Regards
Peter

David

2 April 2015 at 13:42 #51199

Peter, as an example the 3670cc Aston Martin straight 6 in the DB4, fitted with 2 HD8 uses UN needles in 0.125 inch jets. I see the Daimler used UB for a twin set up on a 4500cc straight 6, and UL on a twin set up on 4500cc V8

I wonder if the Bentley 4800 cc 6 cylinder might be the closest analogy to your LG6, using UC or UD needles?

Also do you have copy of the SU needle profile chart ALT9201 which is said to have advice on choosing alternative needle profiles

Julian Messent

8 April 2015 at 08:06 #51206

Hi Peter,
Standard Jag E Type carb specs will get you very close to what you need. You will be able to fine tune on the mixture screws from there.

Very best regards and good luck
Julian

peter weir

5 May 2015 at 20:11 #51243

Hi all
Thanks for your responses, sorry I’ve been out of circulation but the tourist season has started and spare time gets difficult.
There has been a delay as my brand new block was porous and was thankfully replaced f.o.c.
The engine is now built back up and I’ll pass the details to Alan to check what we have and ponder the options.
Regards
Peter

25 September 2017 at 17:25 #52483

Bit late replying to this but may be helpful to anybody looking now or in future. I have 2″ carbs and went through a number of attempts to find the right needles, including having flats filed on the needles installed; all trial and error. Put the car on a rolling road with computer readout (Stanton Motorsport) and see exactly what is happening. Needles chosen accordingly. Result: Heavenly relief!