Needle Carb Fuel Mapper™


General Engine Tuning Warning!

Modifying an engine, carburettor, airfilter, exhaust... can result in: higher performance, reduced performance, or engine failure.

If engine failure occurs, it will be due to an incorrect setup - either a single wrong element, or multiple wrong elements.

Therefore, the engine tuner bears full responsibility for the failure.

Precautions can be taken to dramatically reduce, or potentially eliminate the risk of engine failure.

Where precautions are advised, they should be followed.

Video tutorials for all 'experience levels' are available (or are in production) via

It is advised that the user studies the tutorials, before attempting to modify the carburettor setup, and before an engine is run after modifications have been made.

The advice is given in good faith.



  • What The Needle Carb Fuel Mapper™ does and doesn't do
  • Working With The Software
  • Using The Needle Carb Fuel Mapper™
  • Reporting Bugs


What The Needle Carb Fuel Mapper™ does and doesn't do

General Overview

The Needle Carb Fuel Mapper™ is designed for use with any carburettor using a needle and atomiser.

It calculates the dimensional relationship between the atomiser and the needle, across the entire throttle range.

Together, the atomiser and needle operate as a valve, opening and closing the fuel flow area (the hole gets bigger or smaller).

For each needle/atomiser setup, a graph is produced (fuel map), allowing the user to see how fuel delivery changes at all phases of carburation (at 1% throttle intervals).

What the Needle Carb Fuel Mapper™ does NOT do

   It does not indicate whether the displayed fuel map is correct, for your engine usage - this is achieved by testing.

   It does not 'determine' the adjustment of the fuel flow modifiers - from testing results, it provides an 'indication' of where changes might be made.

   It does not determine fuel consumption - this is determined by all factors associated with the engine and the work it is doing

   It does not stop you from making changes to your engine setup that results in failure!

Study the tutorials for guidance on how best to achieve success and avoid failure.

What the Needle Carb Fuel Mapper™ does do

It provides the fundamental fuel map around which you can plan your tuning.

The fuel map enables you to see:

   The exact throttle position when fuel flow increases

   At what rate the fuel flow area accelerates

   How much of the throttle movement is spent on a static fuel flow area.

   Provides a basis for fuel flow modifier adjustments (comparative to current performance)

   Overlays alternative fuel maps to determine faster fuel delivery, or more (or less) fuel in specific areas of throttle movement

   Enables focussing of attention on specific throttle area problems

   It provides a fixed position upon which changes can be added or subtracted.

Tuning a carburettor without knowing its fuel map, is a process of guessing in the dark, and requires years of experience.

In the past, most people gave up, because they never even gained a starting point to understand how the carb is working.
This difficulty no longer applies.


Working With The Software

The program runs within Microsoft Excel 2007 and later

This is highly beneficial for the tuning community, as the program can be rapidly and constantly updated.

The program cannot function with Open Office nor Libre Office (their programming teams have confirmed this).


1. Create a new folder (eg. in My Documents) called Needle Carb Fuel Mapper.
2. In that folder, create two (sub) folders: 'backup' and 'original'
3. Place the original program file in folder 'original' - don't use it.
4 . Copy the original file to folder 'Needle Carb Fuel Mapper' and rename the file from 'original' to 'working'.
5. Right-click on the 'working' file and choose 'send to' - 'Desktop'.
6. You can drag the desktop icon over the Windows Start Button... after 2 seconds the start menu will open - you can place the launch command into the start menu.

You can now launch the program from your desktop, start menu, or by simply double-clicking the file in its folder.

Special Instructions:  Working with Data!

4 additional command icons have been added to the Quick Access Menu (shown above).
Please identify their location.

These 'command instructions' are provided here, where they can easily be found.
There are help screens in each module, to remind you what you need to do.
For now... just gain a general understanding of the function of these commands.
Their usage will become apparent to you.

Padlock Icon

Clicking this immediately unprotects the software programming.
Click it again - OK - to re-protect the software

Never use the program in unprotected mode, other than to add a new carb name.

# Label Icon

Click this to add your new carb name - OK.

When entering a new carb name - the name should appear in the dialogue box.
If it doesn't, that carb slot has been taken... cancel and move to the next free slot.

Copy Icon

This is a standard copy command.

By using it, you will remember to use the special 'paste-values' icon (the circle icon to the right).

Highlight your chosen data, and click the 'copy icon'.

Paste-Values Icon

Whenever moving data... always copy and 'paste-values'

Do NOT 'copy & paste'.

You will often need to move 'needle and atomiser data', therefore... use this safe technique:

1.  Select your chosen data
2.  Click the 'Copy Icon'

3.  To paste... Click the 'Paste-Values Icon'.

This is good working practice in Excel, when copying data... get into the habit, as it will preserve the appearance of the Fuel Mapper.


Using Needle Carb Fuel Mapper™

Other than entering a new carb name, you probably need little to no instruction.
You've watched the various videos... so just get started.

There are tabs at the bottom that tell you where things are.
When clicking 'save'... when you reload, everything will be exactly as you left it.

Carb Manufacturer Tab

Here all the needle and atomiser information is kept.
Assemble the needles and atomisers that you wish to work with.
Copy the appropriate data and 'paste-values' into the assembly area.
When complete... copy the data and switch to the Carb-Data tab.
'Paste-Values' the data into the next available carb slot.

In the Carb-Data tab
The atomiser, needle and measurement data goes where it says.
In the Tuning Notes... delete what you don't need, and organise it as you wish.

In tuning notes, you will use Ctrl+C to copy, and Ctrl+V to paste.

When adding a new carb... scroll down to the next free carb slot and add all the data.
Clicking the help button brings the help screen, detailing how to add a new name.

1.  Enter any unique name without spaces.
2.  Click on that new name
3.  Click the 'padlock icon' (to unprotect)
4.  Click the '# Label Icon' - OK
5.  Click the 'padlock icon' - OK (to protect)

Add the needle series name in the appropriate place.

Read the help file
You will need to measure a needle in your carb slider.
Also add the carb bore height, or diameter if the bore is circular.

In the Mapper tab
From the drop list at top left, choose your carb... your data is loaded.

Any chosen atomisers left over from the previous carb must be changed to the new atomiser specs.

Two modules are available to you:

Fuel Maps
Maths Module

Scroll to the right to see the Maths Module.
This is controlled from the left side menu, by choosing one or two comparative atomisers, and the throttle position.
The results are indicated in the tables.

You may be more interested in the fuel maps, so scroll back.

Creating Fuel Maps

Find the Needle area.
Find your needle row, and click in a Notch column.
Select your atomiser... the fuel map appears.

You can add many maps at the same time.
They can be switched in and out by the 'tick boxes'.

Working with the Fuel Map

Click on a curve to identify it.
Clicking at specific points will reveal the fuel flow area.

The vertical guide lines are provided to remind the user of the different phases of the carburettor, and where they appear in relation to the fuel map.

Additional  guidelins are provided at top and side.
When required, these can be dragged into place.

When working with fuel maps, certain quirks will exhibiy themselves.
Read below the section on these quirks.

Fuel Map Manipulation Exercises

1. Click on the curve - identify the needle and determine 'fuel flow area' at any point on the curve (the number is % throttle opening)
2. Add curves for your needle and atomiser, at the different notch positions
3. In the needle area - select one of your entries - hit delete.... you do not need to deselect it from the drop box.
4. Choose a needle to graph... using different needles, notches, and atomisers... try to find a different needle that creates a similar curve.
5. Try to find a setup where the curves cross (going richer to leaner or leaner to richer)
6. Try to move the crossover point higher or lower in the throttle range.
7. Grab a spare verticle blue bar from the right, and move it to the crossover point, to indicate the throttle position.
8. Grab a spare horizontal blue bar from the top, and move it over the crossover point, to indicate the fuel flow area at the point.
9. Click the tickbox against a needle, to undisplay its data... click it again to redisplay.
10. Did the graph scale reset itself, destroying the careful positioning of your blue marker lines?... If not, try loading different needle sets, then read 'Fuel Map Quirks' below.

You now know your way around the chart.

Fuel Map Quirks

1.  Curves changing when needles are added

The graph scale must change to suit the needle fuel flow range.
If you load a single, almost parallel needle (tip diameter close to the land diameter) - check the fuel flow area.... not much eh?
Now load a needle with a tiny pointed tip - Boom!... the maximum fuel flow area is enormous by comparison... the scale must change.

If this is a problem (and it can be) when switching in and out needles that you are interested in...
... load a pointed needle on N1 with say the biggest atomiser.
This pushes the curve to the top, and fixes the scale.
You can now load your chosen needles without the graph scale changing.

2.  Strange Curves

Normally you will be working on only one carb, but hey!... you're testing, so you load another carb.
All the curves are immediately wrong.
The atomiser selections have remained from the previous carb.
The last data that you used remains in place... exactly as you'd like for normal use.
So when changing carbs, you must now reselect the atomisers from the new atomiser data set.

3.  Initial curve at start of taper

Sometimes the taper curve precisely angles from the land curve... other times there is a small variation.

This change of curve is due to the throttle being measured in 100 steps.
For a 20mm throttle travel, the measurement is 0.2mm 0.4mm 0.6mm etc.
The start of the needle taper might occur between those measurements.
It's of little consequence.

The taper actually starts at the beginning of the rising curve.

4.  Chart options

In order to allow the chart to be accessed for curve information, and movement of marker lines... the chart had to be left editable.
It is not advisable to mess with any of the settings... and most definitely not the data set.

5.  Go To Chart Data

If you have a lot of carbs loaded, you can go directly to that particular data in the carb data tab (normally you can just click the tab to go to your carb).
When you return to the mapper tab... you must click in say the needle area.
If you click in any of the unselectable areas you will return to the Carb-Data that you just left.
It's a quirk of Excel (perhaps fixed in later versions).

Okay... you are ready to start using the Needle Carb Fuel Mapper™ for tuning purposes.
Oh!... just one other thing....


Reporting Bugs

If you do find a bug... send us an email with 'Bug' somewhere in the subject line.
Try to describe how it occurred.
Thanks for that.

Okay, that's it.
Keep your eye on the website for new info.
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Good luck with your tuning!