9 replies to this topic

[jiminwatford]

I recently had my Mini rolling roaded and was told he modified the needle to richen it up at the top end

 

Watching AC Dodd he seems to mount the needle in a drill and spin it to get an even modification all the way around

 

Mine has been modified with a flat

 

I don't know if this is good or bad. The car runs better than it did but i feel it could run better

 

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[Spider]

I don't see anything wrong with it, but I'll add that I'm not crazy about modifying needles as you can't get a replacement off the shelf.

[nicklouse]

Filing a flat on them is just another way of getting the same result . 

[68+86auto]

At least it is installed in the direction so that it doesn't chew up the jet.

[Steam]

That was how the su gurus used to do it way back, file a flat and check, and repeat.

[ACDodd]

Ok, filing flats in needles is how people used to do it when using fixed needle carbs. The needle would never touch the jet and secondly it was clamped into position and could not rotate, result, filing needles works.
Unfortunately the same methods did not get changed when the su was converted to bias sprung needles. Filing needles on those carbs results in the flat section rubbing in the jet and effectively sawing into the jet and making the jet bigger. Also the needle in bias carbs rotates this has the effect of presenting a different part of the needle to the air stream as it rotates and hence produces the effect of ‘some days it runs really well’.

The point is filing flats on bias sprung needles is not the best way to do things.

Next, the idea that all needles of the same needle code being the same is a falicy. The tolerance on production is 0.0006” wide. When I modify needles about half the time I am removing less than that from the needle to make a fueling change. So I usually carry 4 or 5 versions of the same
Needle. I have on occasions tried 2 or 3 of the same needle to get a better fueling curve simply by working within the tolerance band for the same needle. Indeed I did have one engine where changing the needle for another of the same
Type when from just too rich at part throttle to being ideal.

It is not possible in most cases to take on off of the shelf needle for it to fuel perfectly in applications where you need a replacement simply because the tolerances they are manufactured to are much too wide. 0.0001” on a typical hif44 application at 2 to 3000rpm is measurable in the change in fueling it will deliver. The smaller the carbs become the more sensitive to needle variations they become.

Ac

Edited by ACDodd, 25 March 2024 - 09:47 AM.

[jiminwatford]

 produces the effect of ‘some days it runs really well’.
 

 

This is what i'm finding

 

It's booked in at Mini Medics in July. So hopefully AC can take a look at it then 

[ACDodd]

I look forward to proving which way is best to modify needles!

Ac

Edited by ACDodd, 25 March 2024 - 09:48 AM.

[mini13]

There was a tuner that would pull the needle tick it in a lathe and take some off, ( so it was still cylindrical)  this was mainly for turbo'd motors, as its not really possible to find sutable needles off the shelf for those

[coopertaz]

sadly all this knowledge is being lost and most rolling roads know next to nothing about su carbs. Hope you have apprentices AC Dodd