Dell'Orto VHSB carburetor tool

2022

Aim of the project: Create a tool that will help me sorting out the new jets for my new big bore engine following Rotax MAX Jetting App app.

Description: Having the same engine as one derived from Rotax 125cc karts, and having Rotax released an app that allows you to find the jetting for Dell'Orto VHSB 34 carburettor, the same one used on my engine, I was courious to find out what formulas did they use to obtain the main jet based on the operating conditions.

My engine is based on a Rotax kart cylinder, however it has different specs such as a larger displacement, a different ignition curve and a different exhaust.

So my intent was to create my own model based on the data obtained from the app.

Luckily for me, it was enough to simply download the app APK and decompile it, the variables used were not obfuscated and it was therefore very simple to port the program written in Java to one written in Python to be adapted to my engine.

After this step, to make everything more easily accessible I also converted the program into an Excel spreadsheet and a program that can be used on Maxima.

Dell'Orto VHSB 34 must have this setup:

-K57 needle with the clip on the 3 section from the top

-Air screw need to be 1.5/2 turn out max

-Gas valve 40

-No idle jet

-DP266 pulverizer

-B40 emulsifier

(Stock configuration)

Results: A software capable of carbureting a RotaxMax Kart engine using the formulas of the original app with the possibility of being adapted to your engine specs and configuration.

Original source code of the app decompiled:

Comparison between the original app and the one made by me using the same inputs:

Download available here:

Python: https://github.com/ld-engineering/RotaxMaxJetting/blob/main/RotaxMax%20Jetting.py

Maxima: https://github.com/ld-engineering/RotaxMaxJetting/blob/main/RotaxMAX%20jetting.wxmx

Excel (no possibility to create your own model): https://github.com/ld-engineering/RotaxMaxJetting/blob/main/RotaxMax%20Jetting.xlsx