15 replies to this topic

[gdcarpenter]

Pardon me if this is a stupid question.

I have twin SU2's on my 1990 Mayfair with original Japanese Cooper Conversion and looking to possibly try different needles.

Obviously larger diameter SU's have a bigger throat diameter, so I assume the carb Pistons get larger in diameter as the carb bore increases. It would then seem to me that the larger the carb bore the higher the maximum lift of the carb piston must be to allow full bore opening at Wide Open Throttle.

Is this so?

The reason I ask is that if I were to go from two AAP needles to two AAQ needles, if, as I read somewhere

"In these images, I've selected a working range of '11' measured points along the needle profile, as I don't know if you've got twin HS2's or twin HS4's. If HS2's, then use only the first 9 points

Then with SU2's, do I need only worry about needle diameter up to about station 9. Ergo even if AAQ's continue to get richer and richer beyond station 9 it really wouldn't affect my puny SU2's.

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Edited by gdcarpenter, 10 June 2020 - 12:56 AM.

[sonscar]

With a smaller diameter carb there is less height for the piston to lift.A longer needle may well never come out of the jet?Steve..

[richmondclassicsnorthwales]

The 2 sets of needles are very different in respect that AAP are fixed needles, and the AAQ are biased needles. (Have the spring and a collet for them to sit in the piston)

 

The AAQ will not fit in HS2

 

If you have the Cooper conversion, then the tag number on the carbs should be FZX3052A and would / could have been fitted with H6  AN  M  or  GY needles.

 

These are also a fixed needle, not biased such as the AAQ

[gdcarpenter]

Appreciate the feedback .

This was a John Copper Garages "Anniversary Model" conversion done on the Mini when it was new in Japan by an authorized dealer.

To clarify I have a twin 1 1/4" SU's and the forward carb has a tag that reads "AUD534R'.

The current needles are stamped "AAP" and are clearly spring loaded as shown in the photo.

I marked the highest point on the carb piston, removed it, and measured the maximum lift. I then transferred this measurement to the needle and clearly nothing beyond station 9 is ever going to rise above the jet. Therefore I understand that any needle profile beyond station 9 should never effect the mix.

Seems a "BL" needle would be close to what I am looking for, is the "BL" needle spring loaded?

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[ArnieWallace]

This site might help with choosing the needle. http://www.mintylamb.co.uk/suneedle/

[richmondclassicsnorthwales]

Well, you got me on that one

 

AUD534L / R were fitted to Regent 1300 - 4 Cyl - 1974 motors and indeed used AAP needles, that,s all I know. 

 

Can,t help with the BL needle - sorry

 

Have a look at this link   http://sucarb.co.uk/...sult/?q=aud 534

Edited by richmondclassicsnorthwales, 10 June 2020 - 04:40 PM.

[cockney21]

The 2 sets of needles are very different in respect that AAP are fixed needles, and the AAQ are biased needles. (Have the spring and a collet for them to sit in the piston)

 

The AAQ will not fit in HS2

 

If you have the Cooper conversion, then the tag number on the carbs should be FZX3052A and would / could have been fitted with H6  AN  M  or  GY needles.

 

These are also a fixed needle, not biased such as the AAQ

 

Sorry but this is very wrong, AAP and AAQ are both biased needles and can be interchanged in a HS2 no problem, I swapped my AAP to AAQ in my HS2 twins.

[mad4classics]

The 2 sets of needles are very different in respect that AAP are fixed needles, and the AAQ are biased needles. (Have the spring and a collet for them to sit in the piston)

The AAQ will not fit in HS2

If you have the Cooper conversion, then the tag number on the carbs should be FZX3052A and would / could have been fitted with H6 AN M or GY needles.

These are also a fixed needle, not biased such as the AAQ

Sorry but this is very wrong, AAP and AAQ are both biased needles and can be interchanged in a HS2 no problem, I swapped my AAP to AAQ in my HS2 twins.

Yes, "period" installations would have been fixed needle but any later twin carbs or those re-purposed from another application would be swing. Mine are were originally from A Spitfire MK4 and are swing needle.
Either way stations above 9 will never see use in an HS2.

PS. Does anyone know if the SU needle search tool that was on the mk1-performance conversions web site is maintained anywhere else now?

[nicklouse]

Mintylamb? 

[timmy850]

The needle tool on Mk1-performance was a libre office spreadsheet and it’s a bit convoluted to use. I might have a copy of it on my computer

Mintylamb and Classic Mini DIY websites both have a basic needle comparison chart

[cockney21]

Burlen Fuel Systems (SU) tool is very good, allows you to adjust needle profiles and then will offer the nearest matching off the shelf needle, Works for fixed and swing needles and different jet sizes.  

 

The only true way to get the fuel spot on is to fit a AFR gauge, beats rolling road as you get real world data. I have a twin HS2 on 1293 with SW5 cam, with standard air filter housing AAP are a touch lean, and if you improve the air filters and housing they are too lean, hence my move to AAQ which are pretty much spot on apart from wide open throttle when they go a little rich, which is not the end of the world.   

 

Innocenti fitted the AAP needle as standard to their 1275 which was based on the ADO16 1300GT engine, and the profile very closely follows the standard Cooper S (same carbs and air filter) M needle to about index 6 then goes leaner...probably to limit top end power and improve engine life when driven hard.

 

The standard Cooper air filter housing and filters are a not too good for airflow, especially when the inlet is drawing hot air from the LCB exhaust.

Edited by cockney21, 25 February 2025 - 09:38 PM.

[68+86auto]

The only true way to get the fuel spot on is to fit a AFR gauge, beats rolling road as you get real world data.

 

It's important to watch out for ignition faults causing high O2 instead of a lean mixture causing high O2. It will cause the AFR gauge to read lean when it actually isn't.

[cockney21]

I thought it was the other way...poor combustion will lead to rich mixture reading on the O2 sensor.

[MiNiKiN]

I thought it was the other way...poor combustion will lead to rich mixture reading on the O2 sensor.

E tu, non usare il mio avatar!

   

 

Have you got a link to said Burlen Fuel Systems (SU) tool, please? I failed to find it myself.

 

 

 

[68+86auto]

I thought it was the other way...poor combustion will lead to rich mixture reading on the O2 sensor.

https://www.crypton....issions/O2.html