Su hs4 fixed needle carb. Looking for leaner needle

[robbyasti]

My Innocenti mini 850 was factory fitted with a su hs4 aud 262 carb with fixed needle (AN). (The inno mk2 850 had about 10 bhp more than the standard UK 850). The standard carb has been replaced in the past to an Austin 850 auto hs4 aud 679 carb with swing needle aar.
The carb is in excellent condition but it a little rich for my 850.
Is there a leaner needle that I could replace the fitted aar needle to reduce the consumption or will it make no difference?
Thanks

Rob

[carbon]

Try this excellent website for comparing SU needles: http://www.mintylamb.co.uk/suneedle/

For 850 using HS4 this should be using red spring, and factory used AAV, ABS, and ADH swing needle profiles any of which would be a good starting point for a needle in 850.

AAR is quite a bit richer than any of the above 3 factory needles.

[carbon]

Also AUD679 is listed as HS4 for 1974 998cc, should have had ABX needle. Needle has been changed.

I would also recommend either checking dashpot spring or buying new red spring, this is the one you need.

[robbyasti]

Try this excellent website for comparing SU needles: http://www.mintylamb.co.uk/suneedle/

For 850 using HS4 this should be using red spring, and factory used AAV, ABS, and ADH swing needle profiles any of which would be a good starting point for a needle in 850.

AAR is quite a bit richer than any of the above 3 factory needles.

Thanks for that. Comparing needles on the mintylamb site, the ADH needle that you mentioned is very similar to the AN needle fitted to the standard inno 850 mk2 hs4 carb. The AAP needle is also very similar but slightly leaner than the ADH.
Do you think that the AAP could be too lean, bearing in mind that the inno mini has a little more power than the standard brit 850?
I have the ABX needle in a box of spares that came with the car but according to mintylamb, it is slightly richer than the AAR

[ianh1968]

Try this excellent website for comparing SU needles: http://www.mintylamb.co.uk/suneedle/

... Or

If you have OpenOffice or LibreOffice on your computer, you might want to try
this even more excellent utility for comparing needles.

http://mk1-performance-conversions.co.u ... l_carb.htm

This one has browseable needle charts and several other useful features!

For example #1, it compares by exposed area which is far more accurate.
Most "other" utilities only compare on diameter...

For example #2, if a flat has been filed down a needle, it will tell you what
the round equivalent would be so you can obtain a standard replacement.

For example #3, it will emulate dropping the jet by up to 1/8" so you can
see the differences in fueling that this would introduce.

For example #4, it will automatically choose similar needles to one
you specify, even if it is a "made up" needle.

For example #5, it also has the Zenith Stromberg needles listed, so if
a pukka SU needle cannot be found, one of these could be used instead.
(With simple modifications)

Ian

[mk1]

Thanks Ian,

You beat me to it!

[carbon]

Rob,

My suggestion would be to try an ADH needle, but also fit a new red dashpot spring.

Exhaust can make a big difference to carb mixture, I have a '69 automatic and although it is a standard exhaust going by the sound most of the baffles have rusted away. This needed a new red spring and a richer needle to run properly, before I did this it was really struggling to get above 35mph...

[robbyasti]

Rob,

My suggestion would be to try an ADH needle, but also fit a new red dashpot spring.

Exhaust can make a big difference to carb mixture, I have a '69 automatic and although it is a standard exhaust going by the sound most of the baffles have rusted away. This needed a new red spring and a richer needle to run properly, before I did this it was really struggling to get above 35mph...

Thanks for that. I have checked the spring using the kitchen scales (4.5 oz at 2.65 inches compressed) and I can confirm that it is a red spring.
The ADH needle you mentioned seems to be about right, just a tad richer than the fixed needle AN that was fitted as standard.