Which spring and needle ? – SU HS6 For Landrover series

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:

  1. Copy ACR set up with BGB needle and Black spring
  2. BDM needle with red spring
  3. 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…

needle su

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

Three springs SU HS6

Three springs SU HS6 : the Green, the red and the unknown.. (from right to left)

 

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Needle BDM and BDB fro burlen

 

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Off the Dashpot, and we can easily change the spring and needle

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Replace The spring with the another spring we want

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Off the old needle and the new needle is ready to be installed

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The needle center lead… its funny because actually the needle is slightly not centered even using this centering aid..

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

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Carburetor SU HS6 Set up for Land rover series Part 2

Please read part I here…

This part two is about the selection of needle and spring. When you setting up SU carb for Land rover series, you will have thousand of options to decide which needle and which spring to use…

Why Needle and spring..? because the needle and spring will dictate the attitude of the car, The SU carb is very simple vacuum type carburettor, which can be considered as their strength, needle and spring selection to match with our engine is a very important step and it is very confusing…

Fortunately there are brave hearts that already convert their old Zenith carb, to the similarly old SU carburetor with varying degree of success… some  are using dyno / rolling road to measure the result, some will just use what ever they got on the carburettor and hope for the best. Alternatively you can buy software to select the needle but it beyond the scope of the article

From what I have read, and research… they are few needles candidate to be a good match for land rover series here they are:

BGB needle: this needle used by ACR for their (very expensive) conversion, the BGB needle paired with black spring.

Since they do it to make money for their conversion, I believe they do a lot of (proper) test to come up with this pair. So… it should be the best pair for our land rover series correct..? Yes and may be No. The ACR is offering this conversion together with the performance head, performance camshaft and performance exhaust, so I think that work best on using their set up.

Unfortunately no one (not that I am aware of) is actually using SU HS6 with Black spring and BGB needle on the stock engine. Theoretically BGB needle will be too rich for stock engine.

BDM Needle: this is much leaner needle than BGB, but one land rover forum friend using BDM and red spring set up wich he can describe as working good.

Another candidates are “BBW”, “BDB” few forum lister using it but I am not sure what spring they use but what I have read they have some success using them…

What about my Set up..? well, since I have no money to do a proper research.. so I have to make do with what ever comes with the Carburetor… which is “BAK” with a green spring.

Just to give you the idea the difference for each of the needle candidate, below is chart showing the diameter profile for each needle, before that this is how to read the needle profile:

Imageif we give them number from the top (as position number 1) and to the bottom ( position number 16), you will see the diameter for position number 1 and 2 is for idling, from 3-6 is cruising and from 6 above is revving…

Now lets see the needle profile of all our candidates, see below chart, (if it is too small just click it on the picture). Vertical axis is the diameter of the needle, the higher the smaller the diameter ( means richer fuel), the horisontal axis is the position on the needle

Image

As above you can see, BGB that the ACR used, is the richest of all… BBW comes second so I think BBW can be used for slightly economical than BGB, and number three is my current set up “BAK” needle.

you will also see that the first in position 1-4 the diameter is almost the same for all needles, means that idling and some cruising is almost the same for all needle. the real difference will be after position 4 where some is significantly richer than the others.

Spring: other than needle there are few selection of springs but not as many as needle… Softer spring will easily lift the piston fast, providing more air flow, the stiffer spring will resist of the upward movement providing more fuel enrichment, the idea is to have top maximum carburetor piston lift when the engine is in the top /peak power :

Code Force in Oz. @ Height
Blue 2 1/2 2 5/8″
Red 4 1/2 2 5/8″
Yellow 8 2 3/4″
Green 12 3″
Red & Green 11 1/4 3 7/8″

As above mentioned, from the land rover forum I got confirmation that “BDM” (relatively leaner) needle with Red spring (relatively weak spring) is working sweet. using this as benchmark, my set up : “BAK” (richer than “BDM”) will work OK using green spring (stiffer than red).

I know I am over simplify things but my set up seems OK now… only rolling road will show whether this set up is optimal or not…  I will not give you any suggestion on what set up to use, but you can use the above set up as starting point… I am not the expert, I just taking what I learn and share it

That’s it for now, until then…  take care my aluminum junkies friends… :)

Carburetor SU HS6 Set up for Land rover series Part 1.

In search for the best replacement of original Zenith carb, I found few alternatives, again Internet is helping me a lot. In the spirit of sharing, I would like to share my carburetor set up. I have written: possibly the best carburetor for land rover series few days ago, so I will not cover why I choose SU (skinner union) carb. Here I will explain about the set up, lets start…

Installation is the most complicated one

  1. It requires you to fabricate the manifold / bracket to attach SU carb to your inlet manifold
  2. It needs us to alter the current linkage (to pedal) set up
  3. SU HS6 comes with many type: Left fuel bowl, right fuel bowl, 90* (up right position) and 30* (slightly tilted like in V8 rover)

Those three combination of complexity need us to think, the best placement for the carb. Is it facing to engine, is facing the bulk head or is it facing the radiator fan etc.. Undeterred by this complexity, I go ahead and by second hand SU HS6 and hell broke loose.. :)

Installation: The relatively easy part is buying… I am lucky to get New Old Stock SU HS6 quite cheaply,  so that is good..

SU-HS6

SU-HS6

Now lets make the manifold / bracket or anything you called to attach the carb to inlet manifold. The easiest way is go to a garage that have access on lathe and ask them to set it up for you. for my case I have to go to two different special garage, one is to make the base (two bases as you can see here: one goes to carb and one goes to manifold) the the other garage (exhaust specialist) to make the connection pipe and set it up in the landy. Here is the manifold ready to be installed.

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And finally here is the installed carb… Picture explain better than word.. :)

SU HS6 set up

With this set up I still retain part on the throttle linkage, just in case if I want to change it to zenith again, I still have the parts in there… Hence it installed away from bulkhead and closer to radiator fan. The oil bath filter is still there, although currently it is redundant… but yes you can use the oil bath filter again if you will cross Sahara desert… :)

So that’s all folks… if you have question please ask down below… stay tuned for part two I will talk about setting up the needle, jetting and spring and how it different with Zenith… see you later..