Author Topic: SU needle comparison chart/graph  (Read 147 times)

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Drakman

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SU needle comparison chart/graph
« on: June 26, 2019, 08:55:33 AM »
This may be of interest to those interested in SU carbs and needle selection/comparison.  Probably already here somewhere.

http://www.mintylamb.co.uk/suneedle/

Terry

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Re: SU needle comparison chart/graph
« Reply #1 on: June 26, 2019, 01:32:41 PM »
Hi,

that is fun to play with. Just useful enough to get into all sorts of trouble. :)

Was interesting to see there is not a lot of difference between the ADF and ABX needles which tend to be the two I use the most.

Terry
I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is.


Cujo. 1999 - 2016

Drakman

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Re: SU needle comparison chart/graph
« Reply #2 on: June 26, 2019, 04:36:01 PM »
Hi Terry, 

Yep, i can get into trouble in my sleep, must be something i am just good at.

I have been playing with my SU's.  I am using a twin HS4 setup that i made up from bits and pieces, i thought i was pretty close with AAA needles and the jet turned down 1.5 mm. 

Then i went and fitted an air Fuel ratio gauge.  I keep asking myself "why do i keep doing this to myself" anyway turns out AAA's are too lean after position 6, soooo I made a bias needle holder set the lathe up to use as a guide for the different positions on the needle and wasted way too much time re profiling the AAA's.

If i had that mintylamb thing i could have saved a lot of time and just fitted a set of AAM needles they would only need modifying  at position 3.

It is really interesting to see the effect on the AFR that just a quarter turn on the jet nut makes.

Cheers
Dave

Terry

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Re: SU needle comparison chart/graph
« Reply #3 on: June 26, 2019, 06:22:53 PM »
Drak,

what sort of AFR did you fit?

At least you used and lathe and tried to make accurate modifications. I have needles that have been cut off 1/2 way down or the popular file and emery paper mods made by experts. Makes you wonder why SU waste all that money on precision machinery when all they really need is some 250 paper and a Bastard file.

Terry

Ps. Bastard is actually a particular grade of File that sits between Middle and Second Cut according to Wikipedia. :)
I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is.


Cujo. 1999 - 2016

Drakman

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Re: SU needle comparison chart/graph
« Reply #4 on: June 26, 2019, 07:57:14 PM »
Hi Terry,

 This is the gauge i bought.   
https://www.ebay.com.au/itm/AEM-X-Series-Wideband-02-UEGO-Air-Fuel-Ratio-Gauge-Kit-30-0300/172497892639?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

I figured the lathe would enable me to move between needle positions accurately.  I ended up with both needles nearly identical, only .005 difference on one position.

Haha, I have a file marked "Flat Bastard" someone must have run it over.

Dave

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Re: SU needle comparison chart/graph
« Reply #5 on: June 27, 2019, 08:47:11 PM »
I had a set of twin HS4s on a pretty mild 1310 motor with fixed needles and settled on 6s.  ( a common selection on some mini sites , that and
AO ) .


Drakman if you get a chance and a 5km stretch of road, give it WOT for over 20-30 seconds.  I have seen some SU setups show very good AFRs throughout the rev range and at short WOT, but slowly lean out after this.... which probably doesn't impact the everyday traffic light charger but worth knowing. I think I did the emery paper to last station  ( sorry Terry ) and i did adjust the bridge a smidge. Don't know why it happens, but it was handy to have AFR for it.  I played with some different carbs/setups on this motor and have since swapped out the gauge.
For others interested
From my research wideband sensors of bosch type 4.9 are a) commonly used in dyno shops and aftermarket kit  and b) pretty good- a number of different brands etc. I also think their idle readings can be a bit less reliable- exhaust gases at low rpm from siamesed ports a little bit up and down.