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Unread 09-08-2017, 12:49 AM
emX50's Avatar
emX50 emX50 is offline
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Join Date: Sep 2017
Location: France
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Default Needle Carb Fuel Mapper™

Hello Everybody, and thanks Greg for taking the time to register me

I am an engineer involved in tuning AM6 engines
Most of my posting has been done on the Aprilia RS50 Technical forum - same user name

I've developed a carburettor fuel mapper: Needle Carb Fuel Mapper™

It was developed because it didn't exist, and it seemed to me to be an impossibility to accurately tune the carb without it
The relationship between needle, notch position, atomiser was just a fog of numbers

When it became functional I was truly shocked at the transformation it provided
It's like switching the lights on in a dark room
I've sent Greg a copy - perhaps when he has time, he'll pass some thoughts on it

However, I needed some expert help with Mikuni needles, hence I found this site
If I can gain two dimensions, I can include the entire range of Mikuni needles and atomisers

I'll talk more about that below - first here's an overview of what you can do with the mapper


In order to make predictable changes to the carburettor tune, the fuel map must be understood
Here is an example map of a scenario where a user wishes to modify fuel delivery richer or leaner with a crossover point of 72% throttle

This was achieved using 3 different needles, notch positions, and atomisers
(effectively impossible to achieve by just looking at the component data sheets)

Understanding The Map

Three curves are shown, merely for clarity
Even finer or more radical adjustments can be achieved
  • Each curve can be clicked to identify it and gain specific fuel delivery at any point on the graph
  • Blue guidelines can be dragged into place, to highlight various elements such as throttle regions against fuel delivery
  • A needle row, and notch position is clicked to reveal a dropdown list of atomisers for your carb (the visible numbers)
  • More maps can be selected, and switched in and out by clicking the tickbox
  • Needles can be test mapped and discarded by deleting the atomiser number
Maps can be created in seconds, but the true gain is in how your tuning process is aided

The clarity and accuracy provided, enables clear thinking about specific areas of the throttle phases, and the impact throughout the throttle range that might arise from making any modification

Engine Tuners Perspective

The first key impact is that you can see what you never saw before
  • The exact point when the throttle hits the taper
  • How that point interacts with the cutaway region
  • The impact on the low throttle circuits
  • The change of fuel delivery against more or less airflow
Instead of wasting time & money making a stab in the dark to eliminate that boggy area of the throttle
- you can focus on your current setup, and design another map to address that problem
- then see what changes might be required elsewhere, to balance the new map - say idle circuit or jet adjustment

When the change has been implemented, you know exactly what you have done
Testing the mod can relate to those changes
If it isn't right, but maybe better - the next change can be incremental

But the tuner is in total control.

Beginners & Experts

The expert tuner can immediately consider each element of information and relate it to the physical state of tune (or choice of other jet changes etc.)

The beginner can start understanding carburettor tuning
They still must study the subject (I will be making video tutorials); but at least they are not in a complete fog
Instead of simply giving up (as most do), they stand a good chance of progressing
The fact that they can see the fuel maps, will release their brains to think about what it means, instead of wasting time in a descending spiral of confusion

Tuning Notes

The Carb-Data module has a tuning notes area, so that the current setup can be logged; and thereafter any changes made

Dellorto Carbs

For Dellorto carbs the user can fairly easily add their own carb, whatever it is

Dellorto needles have individual data sheets, but not all the dimensions are provided
The Notch Gap can vary - see diagram above for gaining NG.
'D' the land length is often omitted, but by measuring 'X'... 'D' is revealed

The final measurement is 'Y' - how much of the needle sticks out of the slider.
Count the notches, enter the carb bore, and the carb is added
(copy in atomisers from the supplier site)

Most of this data will be provided, making carb additions a simple affair

Mikuni Carbs - help needed

Mikuni carb component data is completely different
All the data is in one place
The difficulty is that the needle data is obfuscated

We get a general guide - better than the Dellorto system - but the measurements are all taken from the top of the needle
This is irrelevant

The measuring datum edge must be from a notch position
IE. The base of a circlip
Notch 1 - the lowest notch, has been chosen as the datum edge

Therefore, to include all Mikuni carbs, we need to know:
  • The dimension from the top of the needle, to the base of Notch 1
  • The notch gap NG
From these two dimensions, we can calculate the exact position of the needle in the atomiser, for any notch and throttle position
(the user must measure 'Y' - the needle protruding from the slider)

I believe that the tuning community would be very grateful if somebody would be kind enough to take these measurements

I am hoping that all the needle heads are standard - same number of notches, and same notch gap
Any confirmation of this would be greatly appreciated

I have, just yesterday, finally cracked the maths and the programming for all Mikuni single taper needles.
Double tapers are a frightening prospect; but I'll knuckle down

But the key hold up is the needle head dimensions, and experienced knowledge of whether the needle heads are variable

I can promise the suppliers of this information a name reference, or link to their forum name, youtube, or web pages

Commercial web links are fine
The mapper fundamentally encourages people to try different settings, so they should see a bounce in carb component sales

The Current Mikuni Data Set - Warnings!

There are errors in the data sets that are used and displayed around the web.
This included the data set on this site

I don't know who was the first to publish
All the data sets follow the format provided by Ferry Brouwer
His is the most comprehensive - truly first class

How the data was generated is not clear
If measured with an optical gauge, the variations are understandable
However that would have been an enormous project

Yet the taper diameter results are all out by differing degrees
Therefore they cannot have been calculated

The guiding principle is the needle taper angle
It is definitive, so we must presume it to be correct

Everything else is open to error, both in measurement, and simple data entry typos

I am using a repetitive maths calculation, based upon the angles the starting position of the taper, and the needle land diameter

Any variation of the needle diameter and the start of the taper, and the calculations will be wrong

For a 'suck it and see' approach most of the errors are not overly distorting

One needle - 4P3 is completely wrong

The needle tip is indicated as being 2.122 mm D
The actual tip calculates to 0.764 mm D

This can be confirmed when comparing it to the 4L6

3 degrees of taper

4 degrees of taper

The needles are similar length, and the taper starts at a similar length
The 4L6 is a slower taper - 1.19 tip is correct
The 4P3 is a sharper taper - it must be a smaller tip, but it is twice the size


      from correct
4D3	 0.02
4D8	-0.03
4E1	-0.11
4F6	 0.01
4F10     0.03
4F15	-0.02
4J6	 0.08
4J11	 0.08
4J13	 0.02
4L6	 0.01
4L13	 0.11
4P3	 1.36
5D120   -0.18
5E75	-0.03
5F3	-0.13
5F12	-0.07
5F21	-0.11
5J6	-0.09
5J11	-0.06
5L1	 0.00
5J9	-0.01
5N13	 0.02
6F5	-0.10
6F4	-0.10
6F8	-0.14
6F16	-0.09
6F9	-0.02
6L1	 0.01
6N1	-0.05
6F15	 0.17
6F13	-0.09
7F7	-0.00
7F6	-0.06

Any error around 0.1 is quite large

5D120 is a special case

The 5D120 is listed twice in the data set, each with different dimensions
At some point it would be good to clarify that needle

It perhaps arose from a 'sans serif' font, where a 1 and an I are indistinguishable

Over time all these issues can be corrected
But if anybody has these needles, or any of the needles showing errors, we could clear up the confusion before launch


Sorry that this has been a long post... but I hope it was interesting
Thanks for taking the time, if you made it to this point

Hopefully you will see the value of this work, and support my efforts
(€20 I hope will suit all pockets)

Measurements can be made with a vernier gauge, using the jaws and the depth gauge

Here's a quick video dealing with basic carb measurements - the system applies to the Mikuni needle head

Looking forward to hearing your thoughts.
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Unread 11-23-2017, 10:15 PM
170plus 170plus is offline
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Join Date: Feb 2007
Posts: 655

OK. Just seen this - very interesting. I have been looking at some things in a similar way, with basic spreadsheet, but not at the depth you have done.

Measuring a new 6DH7 Mikuni needle with digital verniers, the ND comes out at 0.5mm, and the distance from the top of the needle (at the edge of the needle, above the top groove, ignoring the slight done on the end of the needle) was 5.3mm. The thickness of the 'land' between the notch gaps is 0.45mm - I measured the distance been the opposite edges of 2 x NG's (1.45mm), measured the 'land' width (0.45mm), subtracted that from 1.45mm and divided the result by 2 = 0.5mm. Hope this helps.

Is the Mikuni facility running on your site? If it is, I'll spend the 20 euros!


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