For those who have not read my set up of SU HS6 carburetor for land rover series 3 you can read it Part 1 here and Part Two here:
As you may aware, I bought the carburetor SU HS6 as a complete unit, it comes with BAK needle and green spring, and that what I use for the initial set up… It works but may be not optimal… from the forum and discussion, they are few suggestion:
- Copy ACR set up with BGB needle and Black spring
- BDM needle with red spring
- BDB or BBW but not sure what spring they use..
Just to remind you on the profile of the needle, you can see below that BGB is very rich needle, BBW second, BAK third, BDM fourth and BDB is the leanest…
Actually I want to copy ACR set up, however after having discussion with Burlen… there is no such thing as black spring for HS6, I think they do not want to be copied, and may be they change the color of the spring to hide the their set up…
Finally I ordered BDM and BDB needle and red spring, hence I have three needles and 3 springs (one spring is from old SU)… it will be interesting the try all possible combination.. :).
Here some photos when I am tried needle and spring combination
To make it apple to apple, first I have to make sure that the ignition timing is at 6 deg BTDC as suggested by ACR using their Cyl head.
So.. after the few tries… I finally concluded that the setup is best using green spring and BDB needle... The others also works but at high throttle it missed fire or blow back… or severely lost power compare to this one. it is quite strange… ACR set up is using the richest needle, I am using the same head from ACR but it best using the Leanest of the option…
Bit confuse, but I find it very smooth and have more power using this set up, it capable of going uphill at 3rd gear, previously it need the second gear to climb it… So thats it for now, any questions please write it down below.. hope it can be useful for you
Cheers for now..
Other set up is OK, but in the open throttle, I experienced a missed fire… even if I tried my best to adjust the
Vidinur.net 
Oh, I forgot to mention, with regards to your initial set up with the BAK needle and the green spring, from all my experimenting, trial and error, that set up would provide an extremely over-rich mixture which is why your actual road testing did not go so well. That BAK with a yellow spring would have been fine.
I know this is an old thread, but it is very interesting stuff, and I’ve got some info I can add that may help others. I’ve recently converted my 2.25 petrol to a HS6 SU carb too, and I love it. So much more responsive and seemingly more power for just the same (or better) mpg.
Relating to the needles and springs, I did lots of research and experimenting. HNJ Engineering provide all the parts for the conversion, but I used a new old stock HS6 SU carb I bought off ebay for £60… bargain, and fabricated my own adaptor elbow, cable connections, etc. HNJ Engineering recommend to use a BDL needle with either a green, yellow or red spring. The Green spring is the strongest and provides a richer fuel mixture, whereas the red spring is the weakest and provides the leanest mixture. I actually settled on the yellow spring and the BDL needle. It’s no wonder your set up required the green spring because of using the very lean BDB needle. A yellow spring with the BDM would probably have worked pretty well. These old Land Rovers will run on pretty much any set up, which can make finding the best needle/spring arrangement quite difficult as you can never tell until you do a full road test.
Remember, the weaker the spring, the leaner the fuel/air ratio (many people think that the weaker springs provide a richer fuel/air ratio, but it does not work like that. That is why your lean needle worked better with the stronger green spring. Old Land Rovers with quite thirsty 2.25 petrol engines will usually work better with yellow or green springs. As far as the needles go, similar profiles to the BDL, are BAR, BAK, BES, BBW, BAG. All these needles provide a fairly constant fuel/air mixture gradient and will work well with the yellow spring (red spring also works with these but will run lean). Needles that have a sharp fuel/air mixture gradient drop off such as the BDB, BDM, BEF, BCM, BBH, BFG will struggle with the lean red spring, and will work much better with the yellow or green springs. Yes, I’ve tried all these needles and spring combinations. With the BDL needle and the red spring, my old 1975 LWB Landy was pulling up hills at 30mph in top gear great, but lacked a good top end. This was rectified by replacing the red spring with a yellow spring. I find the Landy very responsive and almost, dare I say, quite ‘nippy’ for an old bus!
Oh, I forgot to mention, with regards to your initial set up with the BAK needle and the green spring, from all my experimenting, trial and error, that set up would provide an extremely over-rich mixture which is why your actual road testing did not go so well. That BAK with a yellow spring would have been fine.