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 Post subject: Needle for 1.5SU - 1275
PostPosted: Wed Apr 08, 2020 9:25 pm 
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848cc
848cc

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Sorry. It’s one of those endless questions, but thought I’d chuck it out there again.

I was looking at an SU needle to suit the following:
- Stock 1275cc from a Morris 1100s.
- 12G940 head
- 1.5” SU on minispares intake manifold
- [edit] standard metal air filter housing
- 1.75” 3to1 extractors (the 3 joins up above the diff
- 1.75” all the way through to standard RC40 side exit

My current needle is bent and I’m trying to roll it out straight again. So I though I might look into something that suits this current setup. It’s a standard road setup. Nothing special. Not looking for more power or anything... just a good all round needle. Wide torque curve would be nice. Lots of hills in Brisbane.

Also, there’s a spring on top of the needle... what on earth is going on there? When I pulled the piston off, I could just wobble the needle... que?

Happy shiny minis people!!!


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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.


Last edited by 3ug3 on Thu Apr 09, 2020 9:31 am, edited 1 time in total.

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PostPosted: Thu Apr 09, 2020 12:18 am 
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848cc
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Standard cam?

The "hanging" needle is an improvement that reduces the wear on the side of the needle. The profile of the side of the needle is the mixture curve, so you don't want that wearing.

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PostPosted: Thu Apr 09, 2020 6:16 am 
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I found a CP4 works fine with a lynx ramflo filter and your manifold.
However this is a fixed needle.
I wouldn't call the floating needle an improvement, they wear themselves and the jet too.

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 Post subject: Needle for 1.5SU - 1275
PostPosted: Thu Apr 09, 2020 9:28 am 
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848cc
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I’m not sure about the cam. I assume it’s also stock.

Forgot... the air filter is standard 1.5SU metal one. I’ll update the list at the top.

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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.


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PostPosted: Thu Apr 09, 2020 10:43 am 
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1275cc
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Location: Camden
The spring-loaded needle was introduced to offer more consistent metering of fuel. If the needle rested against the side of the jet, the area remaining to allow fuel past was more accurate/consistent than having the needle sitting in the centre of the jet and not touching the jet sides, as the early SUs did.
New SUs come with the spring needle arrangement. I don't understand the argument at all, but as Drmini says, they are known for rapid wearing of needle and jet.

I run CP4 needles in twin HS4s on a standard S motor. The needle for a single carb is usually not very different to a twin setup.

The spring needle set up can be converted back to a fixed needle, which offers a larger range of needle profiles.
You will need WZX2003 to fit the needle to the newer piston; but you also need WZX1341 the jet bearing kit for fixed needles.


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PostPosted: Thu Apr 09, 2020 10:45 am 
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1275cc
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The 1275 GT (factory single HS4) in the UK had an AAR swinging/floating needle and red spring.

What needle do you have now?

Some factory examples:
https://www.7ent.com/pages/articles-tec ... eedle.html

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PostPosted: Thu Apr 09, 2020 11:05 am 
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998cc
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I think you may find the main carby body is different between the fixed and floating needles.
The fixed needle body has a larger hole where the brass bit (female needle receptacle) goes into, to allow it be moved around to centre the needle.
This hole is smaller on the floating needle as you don't need the flexibility to centre the jet.
This was on HS6's, from a Marina and Austin 1800.
May not be an issue with the HS4.


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PostPosted: Thu Apr 09, 2020 11:32 am 
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1275cc
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Location: Camden
IndigoBlueCooperS wrote:
I think you may find the main carby body is different between the fixed and floating needles.
The fixed needle body has a larger hole where the brass bit (female needle receptacle) goes into, to allow it be moved around to centre the needle.
This hole is smaller on the floating needle as you don't need the flexibility to centre the jet.
This was on HS6's, from a Marina and Austin 1800.
May not be an issue with the HS4.


I have converted a new set of HS4s from swing to fixed using the jet bearing kit which has a different sleeve to allow the jet bearing to be adjustable for centring.

http://www.minispares.com/product/Class ... o%20search


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PostPosted: Thu Apr 09, 2020 11:45 am 
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848cc
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timmy201 wrote:
The 1275 GT (factory single HS4) in the UK had an AAR swinging/floating needle and red spring.

What needle do you have now?

Some factory examples:
https://www.7ent.com/pages/articles-tec ... eedle.html


Thanks. I was looking at that site. I've got an ADF.

I know it doesn't make that much difference in a road car. I just wanted to research if my bent needle was ok.

I'll try the CP4.

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Australian 69 DeLuxe w/ hydro suspension. Single HS4 (twin HS2 being assembled). 1275 1100s engine (998 due for rebuild) . Clubman remote gear change. Automatic front subframe.


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PostPosted: Thu Apr 09, 2020 12:06 pm 
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1275cc
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If you change to the fixed needle you’ll need the conversion kit like Bill has mentioned

Here is AAR v CP4
Attachment:
1F650872-AB9C-4015-8915-691A1D21EBCB.jpeg


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PostPosted: Thu Apr 09, 2020 2:07 pm 
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1275cc
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Location: Camden
3ug3 wrote:
timmy201 wrote:
The 1275 GT (factory single HS4) in the UK had an AAR swinging/floating needle and red spring.

What needle do you have now?

Some factory examples:
https://www.7ent.com/pages/articles-tec ... eedle.html


Thanks. I was looking at that site. I've got an ADF.

I know it doesn't make that much difference in a road car. I just wanted to research if my bent needle was ok.

I'll try the CP4.


Is your "bent needle" damaged or just leaning over like intended?
I have 2 spring needles from the carbs I converted. They are AAK, if that is close to suitable.
Timmy might be able to find what they might have been intended for and/or compare with AAR on his neat little comparison charts.
Even for a road car, it is important to be close to correct.


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PostPosted: Thu Apr 09, 2020 2:44 pm 
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This is the site, there are a couple of others like mintylamb
https://www.classicminidiy.com/technical/needles


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PostPosted: Thu Apr 09, 2020 8:30 pm 
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Re that graph, the last 3 points on the CP4 are wrong. It's just the needle is shorter? I believe.

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PostPosted: Thu Apr 09, 2020 10:44 pm 
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1275cc
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Location: Camden
One of the SU needle books I looked at list AAF and AAR (and many others) with 16 listed points of measurement at 1/8inch spacing. CP4 only lists 13 points of measurement like many other needles intended for H2 and HS2. The graph had to go to a default setting for the missing 3 measurements giving an odd curve.


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